HFI/NQI 2010
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Europe/Zurich
500/1-001 - Main Auditorium (CERN)
Guido Langouche,
Krish Bharuth-Ram
(University of Kwazulu-Natal)
Description
3rd Joint International Conference on Hyperfine Interactions and International Symposium on Nuclear Quadrupole Interactions
All the preprints from HFI2012 (and also HFI2010) are available on a dedicated mini-site, which can be found here.
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REGISTRATION 500/1-001 - Main Auditorium
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WELCOME DRINK 500/1-001 - Main Auditorium
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Mrs. Itsuko YOSHIDA - Piano concert 500/1-001 - Main Auditorium
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Welcome 500/1-001 - Main Auditorium
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Convener: Reiner Vianden (Physikalisches Institut-Universitaet Bonn)
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Recent developments in Collinear Laser Spectroscopy at ISOLDE, CERN.Optical spectroscopy is known to provide very accurate and model-independent data on spins, electromagnetic moments and charge radii of nuclear ground states. Collinear laser spectroscopy is long known to be a general technique, applicable to a large variety of elements, but was also developed continuously towards higher sensitivity and/or accuracy to scope with even more exotic species. At COLLAPS, the collinear laser spectroscopy setup at ISOLDE, we have applied a frequency-comb based technique to measure the charge radii of the beryllium isotopes including the one-neutron halo nucleus Be-11. Here, high accuracy was required and uncertainties in high voltage calibrations had to be eliminated by simultaneous spectroscopy in collinear and anti-collinear geometry. ISCOOL, a radio-frequency cooler and buncher came recently into operation and was for the first time applied at ISOLDE for the spectroscopy of copper and gallium isotopes and increased sensitivity by orders of magnitude. The isotope chains of both isotopes offered surprises concerning the spin values of the neutron-rich isotopes. Moreover, a new technique combining optical pumping and ß-asymmetry detection was applied for isotope shift shift measurements of Mg isotopes. In this way we were able to cover the chain of Mg isotopes across the complete sd shell to study the nuclear shape development during the transition into the island of inversion. In my talk I will present these methodological developments and the outstanding results that were obtained with these techniques at the COLLAPS experiment.Speaker: Prof. Wilfried Noertershaeuser (Universität Mainz)
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NUCLEAR MOMENTS, NUCLEAR POLARIZATION, NUCLEAR MODELS, FUNDAMENTAL INTERACTIONS 500/1-001 - Main AuditoriumConvener: Reiner Vianden (Physikalisches Institut-Universitaet Bonn)
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10:55
COFFEE BREAK 500/1-001 - Main Auditorium
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Convener: Yorick Blumenfeld (CERN-CERN-CERN)
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NUCLEAR MOMENTS, NUCLEAR POLARIZATION, NUCLEAR MODELS, FUNDAMENTAL INTERACTIONS 500/1-001 - Main AuditoriumConvener: Yorick Blumenfeld (CERN-CERN-CERN)
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Study of Dependence of Quasi-Particle Alignment on Proton and Neutron Numbers in A= 80 Region through g-factor Measurements*Study of Dependence of Quasi-Particle Alignment on Proton and Neutron Numbers in A= 80 Region through g-factor Measurements* Yuan Daqing, Fan Ping, Zheng Yongnan, Zuo Yi, Zhou Dongmei, Zhang Qiaoli, Wu xiaoguang, Li Guangsheng, Zhu Lihua, Xu Guoji, Fan Qiwen, Zhang Xizhen and Zhu Shengyun** China Institute of Atomic Energy, P.O. Box 275-50, Beijing 102413 Email: zhusy@ciae.ac.cn The interplay between the collective rotation and the quasi-particle alignment is a significant feature of nuclear structure at high spins. The g-factors of intra-band high spin states of the ground rotational band can provide direct and unique information on quasi-particle alignment since the g-factors of the high-j proton and the high-j neutron are positively large and negatively small, respectively. The g-factors of high spin states of the ground rotational band in 82Sr, 83Y, 84Zr, 85Nb, 85Zr and 86Zr have been measured in order to study the dependence of quasi-particle alignment on the proton and neutron numbers. The high spin states of the ground rotational band in 82Sr, 83Y, 84Zr, 85Nb, 85Zr and 86Zr were populated by the fusion-evaporation reactions with the heavy ion beams from the HI-13 tandem accelerator at China Institute of Atomic Energy. The transient -magnetic-field ion implantation perturbed angular distribution (TMF-IMPAD) method was used to determine the g-factors of high spin states along the ground rotational band. The model calculations were also carrried out for some nuclides, which well reproduced the experimentally measured g factors. The experimental results are shown in the above figure. It can be seen that for the nuclides 84Zr, 85Zr and 86Zr with Z=40 the proton alignment is followed by the neutron alignment in 84Zr and 85Zr, while the neutron alignment is followed by the proton alignment in 86Zr, and for the nuclides 82Sr, 83Y, 84Zr and 85Nb with N=44 the proton aligns only in 82Sr, the proton aligns first that is followed by the neutron alignment in 83Y and 84Zr and the neutron alignment is followed by the proton alignment in 85Nb. A discussion regard the observed dependence will be presented. *Supported by National Science Foundation of China under Grant Nos. 10435010 and 10975189 ** Corresponding authorSpeakers: Prof. Daqing Yuan (China Institute of Atomic Energy), Prof. Shengyun Zhu (China Institute of Atomic Energy)
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12:25
LUNCH 500/1-001 - Main Auditorium
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SEMICONDUCTORS, METALS AND INSULATORS 500/1-001 - Main AuditoriumConvener: Prof. Hans Hofsaess (University of Goettingen)
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Donor-Acceptor Complexes in ZnOOne of the main obstacles to the technical application of many wide-gap semiconductors represents the difficulty to achieve reliable and sufficient p-type or n-type doping. Possible causes are the electrical compensation of dopants by native defects or other impurities present in the material. For the II-VI semiconductors CdTe, ZnTe, and ZnSe it has been shown [1,2] by perturbed Gamma-Gamma angular correlation spectroscopy (PAC) that the concurrent presence of In donors and group-V acceptors leads to the formation of neighboring donor-acceptor pairs. In case of ZnO, the affinity to form donor-acceptor complexes may help to overcome the limitations of p-type doping of this material as outlined in the theoretically proposed concepts of cluster-doping [3] or co-doping [4]. Here, we report on PAC results obtained by co-doping experiments of ZnO using the donor 111In and different group-V acceptors. Fig. 1 shows a PAC spectrum obtained after the implantation of ZnO with 111In and P and after annealing at 850 K. Besides the lattice electric field gradient (EFG) due to the wurtzite structure of ZnO (nQ Lattice = 31 MHz), two additional EFG caused by the formation of In-defect complexes are observed. They are characterized by two slightly different nearly axially symmetric EFG with nQ1 = 175(1) MHz (Eta = 0.1) and nQ2 = 155(2) MHz (Eta = 0). Due to the wurtzite structure of ZnO having different nearest neighbor distances along the c axis and in the basal plane, respectively, even for identical defect complexes two different EFG are expected to occur. The magnitudes of the EFG observed here are similar to that of the EFG known for In-acceptor complexes in other II-VI semiconductors [1,2]. The nature of the defects in ZnO and the efficiency of different co-doping procedures will be discussed. The results of first PAC experiments on the formation of donor-acceptor complexes using group-VII donors in ZnO utilizing the radioactive donor 77Br will be discussed, as well. This work has been supported by the Bundesministerium für Bildung und Forschung (BMBF) under contract no. 05KK7TS1. [1] V. Ostheimer, A. Jost, T. Filz, St. Lauer, H. Wolf, and Th. Wichert, Appl. Phys. Lett. 69, 2840 (1996). [2] S. Lany, P. Blaha, J. Hamann, V. Ostheimer, H. Wolf, and Th. Wichert, Phys. Rev B 62 R2259 (2000). [3] L.G. Wang and A. Zunger, Phys. Rev. Lett. 90, 256401 (2003). [4] T. Yamamoto and H. Katayama-Yoshida, Physica B 302-303, 155 (2001).Speaker: Dr Manfred Deicher (Technische Physik, Universität des Saarlandes, D-66041 Saarbrücken, Germany)
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Angular correlation studies on 172Lu(172Yb) in GaN and measurement at low temperatureFor optoelectronic devices semiconductors with large band gap doped with rare earth are used. Doping is generally performed during growth but for more structured doping the ion implantation technique is preferable. The perturbed angular correlation technique is an ideal tool to study the annealing behavior of semiconductors after implantation. Usually, this method is only able to measure the absolute value but not the sign of the electrical field gradient (EFG) acting onto the quadrupole moment of the implanted probe. An adequate rare earth isotope for such investigations of semiconductors is 172Yb. The temperature dependence of the hyperfine fields for 172Lu(172Yb) in GaN has been analyzed. The total EFG at the site of this probe is a superposition of the lattice EFG due to the GaN wurtzite structure and the EFG due to the 4f-shell of the rare earth probe itself. The latter is strongly temperature dependent and opposed to the lattice EFG which in contrast is nearly constant since the lattice parameters change only negligibly with temperature. At elevated temperatures all crystal field split levels of the 4f-shell are equally populated. But at low temperatures the lowest level is occupied preferentially. Sign and magnitude of the EFG produced by the 4f shell can be calculated. Depending on which of the levels is lowest in energy it was possible to determine the sign of the lattice field gradient.Speaker: Mr Riccardo Valentini (HISKP der Universität Bonn)
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PAC study of the dynamic hyperfine interactions at 111In-doped Sc2O3 semiconductor and comparison with ab initio calculationsThe combined experimental and theoretical approach based on electric-field gradient (EFG) determinations by means of hyperfine interaction measurements and ab initio predictions at impurity atoms has been shown to be a powerful tool to unravel structural and electronic characterizations of impurities in solids, in particular in semiconductor oxides [1-3]. In this work, PAC experiments using 111In-difussed Sc2O3 polycrystals have been performed at the IPEN facility in order to measure the Electric-Field Gradient (EFG) at (111In (EC)-->) 111Cd nuclei located at the cation site of the semiconductor lattice. The experimental results are compared with ab initio calculations performed with the Full-Potential Augmented Plane Wave plus local orbital (FP-APW+lo) method in the framework of the Density Functional Theory (DFT). The PAC experiments were carried out in the temperature range 10 K – 900 K. The PAC spectra obtained in these measurements shows two very well-defined quadrupole frequencies along the whole temperature range, pointing to the fact that 100% of the probes are located at both nonequivalent cation sites of the bixbyite structure. Nevertheless, the spectra are dampened at certain intermediate temperatures, indicating the presence of dynamic hyperfine interactions that were analyzed with a perturbation factor based on the Bäverstam and Othaz model [4,5]. The FPAPW+lo calculations were performed using the Wien2K code. From the ab initio-experimental comparison, we can conclude that the Cd impurities localized at the axially symmetric D sites of the crystal structure do not present dynamic interactions while that the Cd probes localized at the asymmetric C sites present appreciable dynamic interactions attributed to the so-called after-effects that follow the electron-capture decay of the 111In parent isotope of the 111Cd impurity tracer. This scenario could be supported in terms of the EFG behaviour, predicted by the ab initio calculations, at Cd impurities as a function of the charge state of the impurity located at the different cation sites of the structure.Speakers: Mr Diego Richard (Departamento de Física e Instituto de Física La Plata (IFLP, CONICET-UNLP), Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CC 67, 1900 La Plata, Argentina.), Mr Emiliano Luis Muñoz (Departamento de Física e Instituto de Física La Plata (IFLP, CONICET-UNLP), Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CC 67, 1900 La Plata)
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Temperature dependence of the hyperfine fields of 111In in sapphire (Al2O3) single crystalsThe decay of 111In to 111Cd via electron capture, accompanied by Auger electrons, leaves the outmost atomic shell of the Cadmium in a highly ionized state. In PAC measurements, this so called “electron capture after effect” leads to a significant loss of anisotropy and can be associated with a highly fluctuating electric field gradient (EFG). The recovery of the 111Cd shell by electronic recombination depends on the concentration and the mobility of charge carriers in the material. For insulators, the recombination timescale lies in the nanosecond regime, the generic timescale of hyperfine interaction processes as investigated by the PAC method. In previous measurements the fraction of undisturbed probe atoms showed a strong and reversible dependence on the sample temperature [1]. Our current approach is to determine and alter the conditions under which electrons are sufficiently available to suppress the “after effect”. Sapphire single crystals were ion implanted with 111In at the mass separator in Bonn. After rapid thermal annealing the samples were held at temperatures up to 1000 K. To alter the recombination characteristics and to study the influence of acceptor and donator levels, the samples were additionally doped with several concentrations of Si, Cr and P.Speaker: Mr Michael Steffens (HISKP der Universität Bonn)
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NEW DIRECTIONS, NEW DEVELOPMENTS IN METHODOLOGY 500/1-001 - Main AuditoriumConvener: Prof. Hans Hofsaess (University of Goettingen)
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The Concept of Trajectories in the Data Analysis of Non-axially Symmetric Nuclear Quadrupole InteractionsThe nuclear quadrupole interaction is described as the product of the nuclear quadrupole moment Q with the electric field gradient (EFG) tensor. This is a symmetric, trace-less 3x3 tensor which usually is described by two quantities in the principle coordinate system: the largest component by magnitude is denoted by Vzz and the asymmetry parameter is defined as h = (Vxx – Vyy)/Vzz. Frequently, these two quantities are determined for powder samples as a function of an external variable, e.g. temperature. It is customary to plot both quantities separately versus temperature. This, however, masks any eventual interdependencies of the two quantities. A better way to plot the results is to plot Vzz and Vxx in a carthesian plot, or better in a Czjzek-plot [1], a variant of the carthesian plot, which is still linear in both variables. Each data pair of Vzz/Vxx constitutes a point in this plot with temperature being the implicit parameter. Connecting all points by a continuous line yields a trajectory. This trajectory is continuous even when passing over h = 1 where the tensor orientation flips by 90° and the sign of Vzz changes. Interestingly enough, there are many examples where a straight trajectory is observed, i.e. both variables depend linearly on each other. This can be modelled by a linear superposition of two tensors which are simultaneously diagonal and temperature independent: V = V1 + a(T)V2. The only temperature dependent quantity is a(T), the control parameter. In this situation it is clear that fitting 2n independent parameters for n temperature points is wrong. Instead, a scale factor and a slope should be fitted in addition to n values for a(T), i.e. there are n+2 independent parameters only. The slope is given by the asymmetry parameter of V2, which is the asymptotic asymmetry parameter of V for large a. V2 must have a physical interpretation, contrary to V1 which can be modified by shifting a (unless we know where a must be 0, i.e. if a is an order parameter). The temperature dependence of a contains all solid state information like lattice expansion, lattice vibrations, and changes in the electronic charge density distribution. The correct strategy for the data analysis would be to analyze the data conventionally, plot the data in the Czjzek-plot, and for a straight trajectory perform a simultaneous fit of all data with n+2 adjustable parameters in a second tier. Another interesting class of systems can be described by a linear superposition of two tensors which are not simultaneously diagonal in the same principle coordinate system but which share one common coordinate around which the other two rotate. In other words, only a 2x2 matrix has to be diagonalized. The structure of the resulting eigenvalues (Vieta’s formula) is such that by using the sum and the product of both the control parameter can be eliminated straightforwardly and second order curves result which must be hyperbolae because we require asymptotes. In this case we require n+3 adjustable parameters, i.e. a scale factor, the asymptotic asymmetry parameter and one off-diagonal element which describes the rotation in addition to n values for a. Again, a simultaneous fit of all data is required in a second tier. Examples of experiments with linear and hyperbolic trajectories will be given. [1] G. Czjzek, Hyperf, Interact. 14,184, (1984); T. Butz et al., Physica Scripta 54,234, (1996) Oral presentationSpeaker: Prof. Tilman BUTZ (University of Leipzig)
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15:40
coffee break 500/1-001 - Main Auditorium
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POSTER SESSION MEZANINE
MEZANINE
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COHERENT PHENOMENA, SYNCHOTORON RADIATION, QUANTUM OPTICS 500/1-001 - Main AuditoriumConvener: Pierre Dalmas de Reotier (CEA Grenoble)
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Investigations on thin Fe films and Heusler alloy films using synchrotron-radiation-based Mössbauer spectroscopyRecent development in synchrotron-radiation-based nuclear resonant scattering or Mössbauer spectroscopy has opened up new aspects on investigation of materials in the measurements of hyperfine interactions and also of local phonon density-of-states. In Japan a five-year project led by Prof. Seto at Kyoto University is now in progress for further development of these unique techniques. The field of magnetic thin films is also getting a benefit from these new techniques through detection of magnetic hyperfine fields. The method which has mainly been used so far for thin film experiments is "time domain" measurements, where interference patterns of pulsed X-rays resonantly scattered by nuclei are detected as a function of time. However, "energy domain" measurements are more desirable for thin films, which often contain inhomogeneity in the nuclear environments. In our project, a new synchrotron-radiation-based "energy domain" Mössbauer spectroscopic method has been developed, and optimizeSpeaker: Prof. Ko MIBU (Nagoya Institute of Technology)
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NEW DIRECTIONS, NEW DEVELOPMENTS IN METHODOLOGY 500/1-001 - Main AuditoriumConvener: Pierre Dalmas de Reotier (CEA Grenoble)
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Recent Methodological Developments in Nuclear Resonant Scattering with Synchrotron RadiationA review of progress made in synchrotron radiation based techniquesSpeaker: Dr Esen Ercan Alp (Argonne National Laboratory)
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10:40
COFFEE BREAK 500/1-001 - Main Auditorium
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MAGNETISM AND MAGNETIC MATERIALS: BULK AND THIN FILMS 500/1-001 - Main AuditoriumConvener: Jochen Litterst (TU Braunschweig)
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Magnetism in Iron Implanted Oxides: A Status ReportDiluted magnetic semiconductors form a special class of magnetic materials which has drawn a lot of attention over the last years both for the interest in the basic physics involved and for possible applications, e.g., in the field of spintronics. However, there is no general agreement on the origin of this type of magnetism. Various coupling mechanisms between the magnetic ions have been proposed, in addition the role of intrinsic defects as well as of unintentional magnetic impurities and precipitations was considered. Oxides with embedded magnetic ions form a subclass of the magnetic semiconductors. To study magnetism at the atomic level Mössbauer spectroscopy (MS) can be utilized, especially with 57Fe. Since the solubility of 3d magnetic ions in most semiconductors is small, their introduction is difficult. So, implantation is a favorable technique. In addition it creates intrinsic defects and thus may influence (create) magnetic phenomena. With this idea in mind 57Fe MS was performed at the ISOLDE facility at CERN following implantation of radioactive 57Mn (T1/2 = 1.5 min) in diverse oxides with a focus on ZnO, one of the most important materials for magnetic semiconductors [1]. The Mössbauer spectra obtained consist to a large part of a magnetic sextet with splitting up to about 50 T and in addition of nonmagnetic components indicating different lattice sites and/or charge states of the Fe atoms. Surprisingly the sextet persists up to measuring temperatures of about 600 K. Experiments performed on other oxides (e.g., MgO, Al2O3) show results with partly similar and partly differing features. Detailed MS studies as function of temperature, implanted Mn concentration, pre-doping of the oxides with various magnetic and nonmagnetic ions and in particular experiments with an external magnetic field of 0.6 T show a variety of phenomena with respect to the occurrence of the magnetic fraction and permit attributing it to Fe-ions in a 3+ paramagnetic state. This observation of a static magnetic pattern is enabled by the unusually long relaxation time > 20 ns even at 600 K though this relaxation time normally strongly decreases with rising temperature. Unlike a first report [2] there is presently no necessity to involve ordered magnetism in the interpretation of the magnetic spectra [3]. The assets of MS in these studies compared to, e.g., the EPR technique (Electron Paramagnetic Resonance) will be discussed. References [1] T. Dietl et al., Science 287, 1019 (2000). [2] G. Weyer et al., J. Appl. Phys. 102, 113915 (2007). [3] H.P. Gunnlaugsson et al., Appl. Phys. Lett. (manuscript in preparation).Speaker: Dr Rainer Sielemann (Helmholtz-Zentrum Berlin für Materialien und Energie, D-14109 Berlin, Germany)
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Mössbauer study of spin-lattice relaxations of dilute Fe3+ in MgOT. E. Mølholt1, R. Mantovan2, H. P. Gunnlaugsson3, K. Bharuth-Ram4, M. Fanciulli2,5, K. Johnston6, Y. Kobayashi7, G. Langouche8, H. Masenda9, D. Naidoo9, S. Ólafsson1, R. Sielemann10, G. Weyer3, H. P. Gíslason1 1Science Institute, University of Iceland, Reykjavík, Iceland, e-mail: tem4@hi.is; 2Laboratorio MDM-IMM-CNR, Milano, Italy; 3Department of Physics and Astronomy, Aarhus University, Denmark; 4School of Physics, University of KwaZulu-Natal, South Africa; 5Dipartimento di Scienza dei Materiali, Università di Milano Bicocca, Milano, Italy; 6PH Dept, ISOLDE/CERN, 1211 Geneva 23, Switzerland; 7The Institute of Physical and Chemical Research, Wako, Japan; 8Instituut voor Kern-en Stralingsfysika, University of Leuven, Belgium; 9School of Physics, University of the Witwatersrand, South Africa; 10Helmholtz Zentrum, Berlin, Germany. We have measured 57Fe emission Mössbauer spectra following 50 – 60 keV implantation of radioactive 57Mn+ ( s) at the ISOLDE facility at CERN into MgO single crystals held at 77 – 647 K (Fig. 1). This method allows us to study Fe impurities in concentrations <10-4 at.%. The central part of the spectra (Fig. 1) shows lines from Fe2+ on distorted lattice sites, substitutional sites, and interstitial Fe sites (see [1] for details). The wings of the spectra show what us in focus here; broad distributions of magnetic hyperfine fields up to ~52 T, evidently slowly relaxing paramagnetic Fe3+. These have been analysed/simulated with an arbitrary number of Blume-Tjon (BT) sextets [2] (here a minimum of five BT-sextets was needed, constrained by various common para-meters). The relaxation rate parameter W is allowed to vary with temperature. This parameter corresponds to a spin-relaxation rate of , where is the energy of the Mössbauer state. The (common) change of the BT-sextets is due to increasing values of W with temperature, which as found to increase to 1.5(9) mm/s (assuming mm/s at 77 K). In this range the line shape of the BT-sextets is dominated by broadening of the individual lines by . Figure 2 shows the relaxation rate obtained in this work compared to the results based on EPR measured relaxation rates of dilute Fe3+ impurities in MgO [3]. A reasonably good correlation between the two sets of data is obtained, demonstrating the possibility of retrieving spin-lattice relaxation rates using Mössbauer spectroscopy without the application of an external magnetic field. Other appli-cations of this technique will be given at this conference [4]. References: [1] T. E. Mølholt et al. (2010) this conference. [2] M. Blume and J. A. Tjon, Phys. Rev. 165, 446 (1968). [3] R. S. de Biasi and P. D. Portella, J. Magn. Magn. Mater., 15, 737 (1980). [4] H. P. Gunnlaugsson et al. (2010) this conference.Speaker: Mr Torben Esmann Mølholt (University of Iceland)
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Temperature dependence of the magnetic hyperfine field at 111Cd in ZnO doped with Co.The search for room temperature ferromagnetism in wide band gap semiconductor oxides has been quite intensive in the last years. In particular, ZnO has attracted attention since theoretical calculations[1,2] have indicated that ZnO when doped with a transition metal like Co or Mn should present ferromagnetism at room temperature. The results instead of clarifying this issue have however brought more doubts. While many experimental studies confirm the occurrence of ferromagnetism, several others do not observe magnetic order in such compounds. Hyperfine interactions, by their nature seem to be very suited to investigate these materials and tell something about the existence and origin of the magnetism in such compounds. In the present work powder and bulk samples of ZnO doped with 10 % of Co were prepared by sol-gel method from highly pure metallic Zn(99.9999%) and Co(99.9999%). The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and perturbed gamma-gamma angular correlation (PAC) spectroscopy. In order to carry out PAC measurements carrier-free 111In nuclei were introduced during preparation of the samples and used as probe nuclei in Zn sites. The XRD patterns showed that no second phase appeared and SEM images indicated that the samples are highly homogeneous. PAC measurements were carried out in the temperature range from 50 K to 295K and the results at 295K before cooling down showed that samples of ZnO doped with Co have the same electric quadrupole frequency reported in literature for pure ZnO. This observation indicates that Co ions are substituted for Zn ions and have a similar electronic structure of Zn ions. Below room temperature one of the samples showed a combined magnetic and electric hyperfine interaction from which a magnetic hyperfine field around 1.9 T has been extracted. The temperature dependence of this field showed unusual behavior indicating a first order transition around 300 K which suggests a different type of magnetism.Speaker: Prof. Artur Carbonari (IPEN)
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LUNCH 500/1-001 - Main Auditorium
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MAGNETISM AND MAGNETIC MATERIALS: BULK AND THIN FILMS 500/1-001 - Main AuditoriumConvener: Yutaka Yoshida
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Magnetism in Azurite Studied by Muon Spin RotationThe natural mineral azurite Cu3(CO3)2(OH)2 represents a new type of low-dimensional frustrated quantum spin system with a diamond spin chain as basis. From specific heat [1] there is evidence for a phase transition at ca. 1.8 K which however is magnetically still ill-defined. Earlier muon spin rotation experiments [2] have indicated a magnetic transition yet no systematic study has been reported. We have performed zero field and transverse field muon spin rotation experiments at Paul Scherrer Institut Villigen (Switzerland) in the temperature range from 0.02 K to 6 K on polycrystalline powder and a single crystal. We could corroborate the appearance of magnetic order below 1.9 K from spontaneous muon spin rotations with frequencies following a magnetization curve indicating 2-dimensional correlations. There is evidence for a further change in magnetic structure below about 500 mK. The ordered magnetic Cu moments can be estimated to be only on the order of some tenths of a Bohr magneton in agreement with recent neutron scattering data [3]. References [1] H. Kikuchi, et al., Phys. Rev. Lett. 94, 227201(2005). [2] H. Kikuchi, et al., Progress of Theoretical Physics Supplement. 159, 1 (2005) [3] K. Rule, et al., Phys. Rev. B 81 in print (2010)Speaker: Jochen Litterst (TU Braunschweig)
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Defect induced magnetic interaction in highly oriented pyrolytic graphite (HOPG): A local investigation using TDPAD methodDefect induced magnetic interaction in highly oriented pyrolytic graphite (HOPG): A local investigation using TDPAD method. S.N. Mishra,1 S.K. Mohanta,1,2 S.K. Srivastava2 1Dept. of Nuclear and Atomic Physics, Tata Institute of Fundamental Research, Mumbai-400005, India, e-mail: mishra@tifr.res.in 2Dept. of Physics and Meteorology, Indian Institute of Technology, Kharagpur-721302, India Defect induced magnetism in carbon based systems have long been the subject under extensive investigation, not only for the nature of magnetism in s, p electron systems but also for its potential to practical applications. The discovery of ferromagnetism at room temperature in pure carbon materials has given a new impetus for magnetic studies in graphite and other carbon materials [1,2]. It has been suggested that defects play a key role for the ferromagnetic ordering observed in graphite. Here, we present magnetic hyperfine field of 19F measured by time differential perturbed angular distribution technique. The 19F probes were produced via the heavy-ion reaction 12C(12C,αp)19F using pulsed 12C beam at an energy of 40 MeV. The energetic 12C beam impinging on a 1 mm thick HOPG sample, used as the stopper, also creates high concentration of defects. The approach adopted here, thus serves the dual purpose of creating defects and studying the magnetic interactions arising thereof. For the detection of hyperfine fields we have used the 5/2 isomeric state in 19F with half-life T1/2=88.5 ns, g-factor gN = 1.44 and, quadrupole moment Q = -0.12 b which offers high sensitivity towards magnetic interactions. Typical spin rotation spectra R(t) measured for 19F in HOPG are shown in Fig 1. The R(t) spectra show superposition of two frequencies having L = 64 and 93 MHz and intensity ratio of 45:55 at 15 K. Fig 2 shows the temperature dependence of the magnetic hyperfine field Bhf derived from the expression Bhf = (L/gNNBext)-Bext. The L for the two components show distinctly different temperature dependence yielding Bhf ~5 kG and 0.8 kG at T = 0. The observed results indicate the presence of strong magnetic interaction in HOPG. Supported by ab-initio calculations performed for a number of defect configurations around a F impurity in graphite, we assign the high field component to substitutional site with single vacancy/interstitial C, and the low field component to F at substitutional/interstitial sites without any vacancy in its neighborhood. Fig 1. Spin rotation spectra at 15 and 35K . Fig 2. Hyperfine field as a function of temperature. References [1] T. Makarova et al., Carbon based magnetism, Amsterdam: Elsevier; p. 371-96 (2006). [2] P. Esquinazi et al., Phys. Rev. B 66, 024429 (2002).Speaker: Prof. S.N. Mishra (Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai-400005, India)
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COFFEE BREAK 500/1-001 - Main Auditorium
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POSTER SESSION MEZANINE
MEZANINE
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ISOLDE/LHC TOUR 500/1-001 - Main Auditorium
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NEW DIRECTIONS, NEW DEVELOPMENTS IN METHODOLOGY 500/1-001 - Main AuditoriumConvener: Haraldur Gunnlaugsson (Aarhus University)
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SURFACES, INTERFACES, THIN FILMS, NANOSTRUCTURES 500/1-001 - Main AuditoriumConvener: Haraldur Gunnlaugsson (Aarhus University)
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Development and applications of a Mössbauer cameraWe developed a mapping technique for 57Fe Mössbauer spectroscopy using a Multi-Capillary X-ray lens (MCX or Soejima-Kumakhov lens), which provided a space resolution down to 50m [1, 2]. There are, however, strong demands to study sub-micrometer-scale structures in materials science. Presently, we are challenging to improve the space resolution using a Fresnel-Zone Plate (FZP), which is known to provide a possibility to focus X-ray beam down to several 10 nm in diameter, if one would use it at a beam line of synchrotron facilities where a strong and sharp X-ray beam is available. In our laboratory, therefore, we combine a FZP with the MCX in order to focus 14.4keV -rays down to hundreds nanometers. The focal distance is 48 mm from the outlet of FZP lens. The experimental or and 3.7 GBq-57Co source mounted on a Mössbauer transducer. In order to evaluate the spot size of the combined -ray lens, the transmission counts of 14.4keV -rays are measured as functions of the X or Y positions of the Ta-knife-edge collimators by a Si-PIN detector. The measuring time is 55000 sec at each position. After subtracting the background from the original data (red points in Fig.2), we obtained the blue data points which shows two sharp peaks of the 1st order diffraction at around 155m close to the beam center. In addition, two broad peaks appear at around 125 and 75 m, which correspond to the 2nd order diffractions. The position of the Ta knife-edge appears to be about 10m deviated to the direction of the FZP from the exact focal position. Considering the focusing geometry and the half-width of the sharp peaks, the spot size expected at the focal position can be estimated about 3m in diameter. The mapping images will be shown in the lecture.Speaker: Mr Yoshida YUTAKA
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Quadrupolar Perturbed NMR in Inorganic NanomaterialsInorganic nanostructures reveal a number of applications in electronics, magnetic recording, as low-friction and nano-bio materials. However, our knowledge about properties of inorganic nanomaterials is still limited. Quadrupolar perturbed NMR is an excellent tool in studying the local site symmetry, chemical bonding and electronic structure of inorganic nano-particles comprising quadrupole nuclei. I will review my own and literature data on NMR spectra and relaxation measurements of quadrupole nuclei in several inorganic nano-compounds such as boron nitride nanotubes, vanadium oxide nanotubes and molybdenum sulfide fullerenes. Detailed analysis of the spectra and their comparison with those in bulk samples will be done. The obtained findings allow us making conclusions about the local crystal structure, electronic structure and bonding in the inorganic nanosized compounds.Speaker: Prof. Alexander Panich (Ben-Gurion University of the Negev)
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10:40
COFFEE BREAK 500/1-001 - Main Auditorium
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LATTICE DYNAMICS, ION-SOLID INTERACTIONS 500/1-001 - Main AuditoriumConvener: KO MIBU
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Density of Phonon States at the Fe Sites in Superconducting FeSe as Function of Temperature and PressureThe temperature and pressure dependence of the partial density-of-phonon states (phonon-DOS) at the iron sites in superconducting (sc) Fe1.01Se was studied by 57Fe nuclear inelastic scattering (NIS) of synchrotron radiation, a method well adapted for these studies as function of temperature and pressure [1,2]. As proved by a recent study of the isotope effect at the Fe sites on the sc temperature Tc in FeSe, superconductivity is intrinsically connected with the Fe phonon modes [3]. The sc properties of the present Fe1.01Se sample and their pressure dependencies were well characterized in previous studies using various methods, including 57Fe-Mössbauer spectroscopy [4-7]. The high energy resolution in the present 57Fe-NIS study allows for a detailed observation of spectral properties in the phonon-DOS not observed before, e.g. shifts of all spectral features to higher energies by ~4% with decreasing temperature from 296 K to 10 K. No detectable changes in the partial Fe phonon-DOS were observed at the tetragonal–orthorhombic transition around 100 K [7,8]. An applied pressure of 6.7 GPa, combined with an increase of the sc temperature Tc from 8 K to 34 K [8], resulted in an increase of the optical phonon-mode energies by ~12%, and an even more pronounced increase in energies of the lowest-lying transversal acoustic modes. Despite of these strong pressure-induced changes in the partial Fe phonon-DOS we conclude that the pronounced increase of Tc in Fe1.01Se with pressure cannot be described in the framework of classical electron-phonon coupling [8]. This suggests the importance of spin fluctuations for the observed superconductivity [9]. The present results are discussed in conjunction with the phonon-DOS of FeSe0.5Te0.5 X-tals, studied including its polarization dependence by 57Fe-NIS [10], where Tc = 15 K was observed at ambient pressure. Finally we present a synopsis of the complementary information on the sc Fe1.01Se and FeSe0.5Te0.5 systems, obtained from the elastic channel, 57Fe-ME [4-7], as well as from the inelastic channel, 57Fe-NIS [8, 10], of the 57Fe(14.4 keV)-Mössbauer resonance. References: * wortmann@physik.upb.de [1] A.I. Chumakov et al., Phys. Rev. B 54, R9596 (1996). [2] R. Lübbers, H.F. Grünsteudel, A.I. Chumakov, G. Wortmann, Science 287, 1250 (2000). [3] R. Khasanov et al., arXiv:1002.2510.v1. [4] T.M. McQueen et al., Phys. Rev. B 79, 014522 (2009). [5] S. Medvedev et al., Nature Mater. 8, 630 (2009). [6] V. Ksenofontov et al., contribution to this conference. [7] T.M. McQueen et al., Phys. Rev. Lett. 103, 057002 (2009). [8] V. Ksenofontov et al., Phys. Rev. B (in print); see arXiv:1004.2007. [9] T. Imai et al., Phys. Rev. Lett. 102, 177005 (2009). [10] V. Ksenofontov, G. Wortmann, T. Gasi, J. Deisenhofer, V. Tsurkan, C. Felser (unpublished)Speaker: Prof. Gerhard Wortmann (2Department Physik, Universität Paderborn)
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12:30
LUNCH 500/1-001 - Main Auditorium
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CONFERENCE EXCURSION Annecy
Annecy
CH - 1211 Geneva 23 SwitzerlandTour of Annecy (France)
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SEMICONDUCTORS, METALS AND INSULATORS 500/1-001 - Main AuditoriumConvener: Kensaku Matsuta (Osaka Univ.)
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BIOLOGY, CHEMISTRY, MEDICINE, ARCHAEOLOGY, MINERALOGY 500/1-001 - Main AuditoriumConvener: Kensaku Matsuta (Osaka Univ.)
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Ab Initio Hyperfine Interactions as a Powerful Tool to Identify the Metal Binding Site in Biological Systems: Cd2+ in DNA Bases.Hyperfine interactions can be a powerful tool to identify local environments in many different systems. Recently it has been drawn attention to the possible application of the Time Differential Perturbed Angular Correlation (TDPAC) technique to study differences in the Nuclear Quadrupole Coupling constants ( υQ ) at Cd probes in mouse DNA infected with the Trypanosoma Cruzi. The electric contribution to the hyperfine interaction is usually expressed as the nuclear quadrupole coupling frequency υQ which is given by the product of the nuclear quadrupole moment Q and the Electric Field Gradient (EFG) at the nucleus. The EFG can be theoretically obtained from an ab initio electronic structure calculation. The 111In → 111Cd β decay can be used in a TDPAC measurement to investigate the Cd metal binding to DNA. The interaction of the metal with the DNA bases can change many aspects of the base pairing [1]. Here we study electric hyperfine properties of Cd bound to some DNA bases. The methodology used for the electronic structure calculations is based on the Kohn Sham [2] scheme of the Density Functional Theory (DFT) and the Car-Parrinello [3] method. We use the Projector Augmented Wave [4] method as embodied in the (CP-PAW) computational code. The results of EFG and energies are discussed as function of water molecules present in the Cd²+ environment and compared with TDPAC measurements at Cd probes in mouse DNA infected with the Trypanosoma Cruzi.References [1] J. V. Burda, J. Sponer, J. Leszczynski, P. Hobza, J. Phys. Chem. B., 101, 9670 (1997). [2] W. Kohn, L. J. Sham, Phys. Rev. B., 140, 1133 (1965).[3] P. E. Blöchl, Phys. Rev. B., 50, 17953 (1994).[4] R. Car e M. Parrinello, Phys. Rev. Lett. 55, 2493 (1985).Speaker: Mr Philippe Alexandre Divna Petersen (Universidade de São Paulo)
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10:40
COFFEE BREAK 500/1-001 - Main Auditorium
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NEW DIRECTIONS, NEW DEVELOPMENTS IN METHODOLOGY 500/1-001 - Main AuditoriumConvener: William Evenson
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Recent advances in Emission Channeling measurements and relevance to Hyperfine InteractionsHyperfine interactions are due to the coupling of the nuclear quadrupole and magnetic moments with the electric field gradient and magnetic fields present inside a material, respectively. “Hyperfine Techniques” can then deliver unique information to enlighten atomic and electronic phenomenology on a nanoscopic scale, provided their signal will be fitted with the right model and then properly interpreted. During the last two decades big advances have been made for the interpretation of hyperfine data. Powerful first principle calculation methods of charge densities in materials provide today reliable tools for the interpretation of hyperfine parameters. Still, these methods rely on establishing an atomic model with the only input of the initial atomic coordinates, which are then allowed to relax to more energetically favorable positions. This brings us to the point that, since the hyperfine parameters are extremely sensitive to both relaxations and the atomic position of the probing atom, a technique that can provide precise local scale information about impurity element position can be of great use for the modeling of the atomic configurations used to interpret the hyperfine parameters. This talk introduces the emission channeling (EC) technique, which uses the fact that charged particles (in this case electrons), emitted from implanted radioactive isotopes, are guided by the potential of atomic rows and planes while traveling through a single crystal. The resulting anisotropic electron emission patterns around low-index crystal directions are characteristic for the lattice site occupied by the emitting atom and are measured with a 2-dimensional energy- and position-sensitive Si detector of 22 × 22 pixels. This technique allows one to measure the lattice location of a very low concentration of impurities with accuracy down to 0.1 Å. The combination of position sensitive detectors developed at CERN in the frame of high-energy particle detection with the ISOLDE radioactive beam facility provides a huge number of radioactive element probes to be measured with high precision. Selected case study examples will be shown as well as the perspectives for improving this technique with new highly pixilated electron detectors recently developed at CERN.Speaker: Dr J.G. CORREIA (ITN, Sacavem, Portugal)
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NUCLEAR MOMENTS, NUCLEAR POLARIZATION, NUCLEAR MODELS, FUNDAMENTAL INTERACTIONS 500/1-001 - Main Auditorium
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Resonance Methods 500/1-001 - Main Auditorium
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NEW DIRECTIONS, NEW DEVELOPMENTS IN METHODOLOGY 500/1-001 - Main AuditoriumConvener: William Evenson
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Entanglement in nuclear quadrupole resonanceQuantum systems in an entangled state [1] can be used as a primary quantum information channel to perform computational [2], communicational [3], metrological [4, 5] and cryptographic tasks that are impossible for classical systems. These possible applications of entangled quantum states stimulate intensive research in the fields of generation and manipulation of them. Entangled states may appear in various systems of interacting quantum particles, such as phonons, ions, electron, nuclear spins, and of a single particle interacting with environment. We study entanglement between quantum states of multi level spin system of a single particle considering a nucleus with spin 3/2 in both the internal electric field gradient and the external magnetic field. It was shown that entanglement is achieved by applying a magnetic field to a single particle at low temperature ( 5 mK). In this temperature range, the numerical calculation revealed the coincidence between magnetization and concurrence. As a result, the magnetization can be used as an entanglement witness for such systems. 1. C. H.Bennett , G.Brassard , C.Crepeau , R.Jozsa , A.Peres , and W. K.Wootters , Phys. Rev. Lett. 70, 1895 (1993). 2. C.H. Bennett and G.Brassard , Proceedings of IEEE International Conference on Computers, Systems and Signal Processing, Bangalore, India, pp. 175-179, December 1984. 3. P.Shor, in Proceedings of 35th Annual Symposium on the Foundations of Computer Science (IEEE Computer Society, Los Alamitos, CA, 1994), p. 124-134. 4 P. Cappellaro , J. Emerson , N. Boulant , C. Ramanathan , S. Lloyd , and D. G. Cory , Phys. Rev. Lett., 94, 020502 (2005). 5 C.F.Roos, K.Kim, M.Riebe, R. Blatt, Nature 443, 316 (2006).Speaker: Prof. Gregory Furman (Ben Gurion University)
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12:30
LUNCH BREAK 500/1-001 - Main Auditorium
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BIOLOGY, CHEMISTRY, MEDICINE, ARCHAEOLOGY, MINERALOGY 500/1-001 - Main Auditorium
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Proton Dynamics in One-dimensional Hydrogen-bonding System in Molecular Co-crystals TMP-D2ca and DMP-H2caRecently, hydrogen-bonded supramolecular co-crystals have attracted much interest in aim for functional materials such as ferroelectrics [1]. By use of 35Cl nuclear quadrupole resonance (NQR) we have studied an organic ferroelectric, phenazine(Phz)-chloranilic acid (H2ca) co-crystal, Phz-H2ca, and found an electric field gradient fluctuation probably due to a proton dynamics in hydrogen bond [2]. For the detection of rather slow motion of proton in the hydrogen-bonding system, NQR spin-lattice relaxation of the nearby atom will be quite sensitive. In the co-crystal of tetramethylpyrazine (TMP) with H2ca, TMP-H2ca, the spin-lattice relaxation time (T1) of 35Cl NQR showed a steep decrease with increasing temperature above ca. 250 K. The decrease could be explained by the Arrhenius law with the activation energy of 35 kJ mol-1 [3]. In the present paper we studied a possible proton motion in another compound with a similar one-dimensional hydrogen bond, DMP-H2ca, the co-crystal between 2,6-dimethylpyrazine (DMP) and H2ca. The isotope effect on the hydrogen motion by deuteration of the acid hydrogen in TMP-H2ca was also studied. Fig. 1 shows temperature dependence of 35Cl T1 of TMP-D2ca compared with that of TMP-H2ca. By the deuteration the activation energy increased to 50 kJ mol-1. The deuteron motion was confirmed by 2H NMR spin-lattice relaxation measurements which resulted in the activation energy of 49 kJ mol-1. Fig. 2 shows temperature dependence of 35Cl T1 of DMP-H2ca. In this compound the relaxation is dominated by lattice vibration suggesting no transfer motion of proton between the acid and base molecules. References [1] S. Horiuchi and Y. Tokura, Nature Materials 7, 357-366 (2008). [2] T. Asaji, J. Seliger, V. Žagar, M. Sekiguchi, J. Watanabe, K. Gotoh, H. Ishida, S. Vrtnik, and J. Dolinšek, J. Phys.: Condens. Matter 19, 226203 (2007). [3] T. Asaji, Y. Yoshimura, and D. Amino, Hyperfine Interact. 179, 1-7 (2007).Speaker: Prof. Tetsuo Asaji (Nihon University)
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Convener: Stephan COTTENIER
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DFT Study of Hyperfine Interactions in Some Types of the ComplexesIt is well known that chemical applications of the NQR and Mössbauer spectroscopies use the sensitivity of the experimental parameters to investigate changes in the electron density at the nucleus [1]. The nuclear quadrupole constants and isomer shift are a function of both nuclear and electronic properties of the molecular systems, which are combined in such a way that independent quantitative information on both kinds of properties cannot be obtained by NQR and Mössbauer spectroscopy alone. Since the electronic properties are usually of interest and because the nuclear parameters are constant, the hyperfine parameters are most frequently used to compare the electronic properties of different molecules. The covalent effects and the shielding of one set of electrons by another also influence the electronic environment of the nucleus and may be reflected in changes in the isomer shift. On the other hand central to most simple theories of Lewis acidity is the idea that both ionic and covalent interactions play important roles in stabilizing the donor-acceptor bond [2]. In this report, we present a DFT calculations based on a microwave spectroscopic, nuclear quadrupole resonance and Mössbauer shifts of the donor-acceptor complexes formed from metal halides such as PtCl2, PtCl4, XeF2, AuCl, AuCl3, SbCl5, SnF4, SnCl4, TiCl4, SnBr4, NbCl5, TaCl5 , halogens and interhalogens with organic ligands. All ligands have a different basicity and softness. Therefore, it is of interest to investigate these complexes with a different acids and to compare their structural and electronic properties. The full optimization of geometry was carried out using B3LYP achieved within the GAUSSIAN’03 program. The calculations of the complexes were carried out with all-electron DGDZVP basis set. The quadrupole coupling constants of the quadrupole atoms and the formation energy of the complexes has been broken down using the extended transition state (ETS) scheme implemented in the ADF package. We have used the OPTX exchange functional combined with PBE correlation functional with an uncontracted STO triple- + polarization basis set using the frozen core approximation to treat the inner electrons. There are bases to consider, that the relativistic effects basic for such heavy atoms should be considered by the zero order regular approximation (ZORA) that is more reliable than the widely used Pauli formalism. An analysis of the quality of the calculations that employ all-electron basis set for the halogen compounds was carried out. The ZORA method is shown to be a viable alternative for the calculation of halogen coupling constants in molecules. In addition, the ZORA model, in contrast to the pseudo-potential model, leads to realistic values of all metal nuclear quadrupole coupling constants [3]. The calculated energy terms can be identified with three main components of the chemical bond, i.e. Pauli repulsion, electrostatic attraction and covalent interaction. As a result, we receive the answer to a question about the relative contributions of covalent and electrostatic interactions to the donor-acceptor bond. If for the transition element complexes the electrostatic bonding is larger than covalent bonding while for the non-transition element complexes the tendency opposite. The obtained result will be coordinated to the conclusion on the basis of Klopman approach. In the language of the theory of hard and soft acids and bases, the calculated energy gaps involve direct mixing of the donor and acceptor orbitals. Energy of the bonds, calculated from the general energy of molecules with ZPE corresponded as formation energy of the ETS scheme, and to experimental enthalpy of the complex formation. The obtained dependences between Mössbauer chemical shifts and populations of the central atoms pointed to another nature of the chemical shifts in transition compounds in comparison with non-transition element compounds. Besides, the values of the valence electron charge density at the nucleus 0 have been evaluated from ZORA calculations for a number of Au, Pt, Xe, Sn, Sb, I compounds in order to check the accuracy of the theoretical approach. The linear correlations between the experimental values of δ and the calculated values of 0 is obtained. [1]. Parish R. V. Coord. Chem. Rev., 1982, V. 42, P. 1. [2] Frenking G., Wichmann K. et al. Coord. Chem. Rev., 2003, V. 238-239, P. 55. [3] Poleshchuk O. K., Branchadell V., Ritter R. A., Fateev A. V. Hyperfine Interactions, 2008, V. 181, No. 1-3, P. 27.Speaker: Prof. Oleg Poleshchuk (Tomsk State Pedagogical University)
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MAGNETISM AND MAGNETIC MATERIALS: BULK AND THIN FILMS 500/1-001 - Main AuditoriumConvener: Stephan COTTENIER
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Low Temperature Nuclear Orientation Studies of the Magnetic Structures of RNiAl4 in Applied Magnetic FieldsThe family of metamagnetic compounds RNiAl4 (R = rare earth) exhibits a range of interesting magnetic behaviours. There are multiple magnetic phases, and crystal field driven differences in anisotropy and behaviour when different rare earth ions (R) are present in the compound. TbNiAl4 is one illustrative example. It has two phase transitions (three phases) as a function of temperature in low applied magnetic field, and also at least three phases as a function of applied magnetic field at low temperature [1]. Aligned with the first of these field driven transitions is a large inverse magneto-caloric effect (MCE) [2]. Recent neutron diffraction studies carried out on single crystal TbNiAl4, in applied magnetic fields, show the onset of an incommensurate antiferromagnetic ordered phase above the first field induced phase transition [3]. This observation vindicates the existence of the higher entropy state at higher applied field that is required for an inverse MCE but contradicts the predictions of other authors who suggest a spin flop transition [4]. Low Temperature Nuclear Orientation (LTNO) can also be usefully applied to TbNiAl4 and other RNiAl4 compounds to investigate magnetic structure. In the case of the Tb compound, neutron activation is used to create in situ 160Tb LTNO probes. However, as we found recently, TbNiAl4 crystals must be annealed after thermal neutron irradiation in order to remove damage and restore full gamma-ray anisotropy [5]. In this paper, we present new LTNO results for annealed TbNiAl4, in applied fields extending to 9 tesla. These results support the model of magnetic struture revealed by the earlier neutron diffraction studies. LTNO is also applied to crystals of compounds with R = Nd and Pr. These additional studies magnetic fields sufficient to traverse the respective first metamagnetic transitions were also used and behaviours similar to the TbNiAl4 case were observed.Speaker: Wayne Hutchison (University of NSW at ADFA)
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Perturbed angular correlation study of the magnetic and structural first-order phase transition in MnAstext + referencesSpeaker: J. N. Gonçalves (Departmento de Física and CICECO, Universidade de Aveiro, 3810-193 Aveiro, Portugal)
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Anomalous Magnetism and 209Bi Nuclear Spin Relaxation in Bi4Ge3O12 CrystalsUnique magnetic properties were earlier found by measuring the NQI parameters in a number of bismuth (III) oxy compounds with s- and p-electrons hitherto classified as diamagnetic [1]. In α-Bi2O3 single crystal the magnetoelectric effect and paramagnetism depending on magnetic prehistory of the sample were observed [1]. In Bi4Ge3O12 (BGO), local magnetic fields (Hloc) of the order of 20-30 G were found by modeling the Zeeman split 209Bi NQR spectra and spin-echo envelope [2-3]. A dramatic increase in the 209Bi line intensity was observed for this compound in the Zeeman fields (He ) hence revealing a remarkable elongation of the nuclear spin-spin relaxation time T2 under the influence of He [4]. This stimulated relaxation studies of the BGO crystals doped with the “magnetic” atoms Cr, Nd, Pr, Gd. Here, we present the results of a study of the 209Bi nuclear quadrupole spin-spin and spin-lattice relaxation in pure and doped BGO single crystals in the temperature range 4.2300 K. Various mechanisms (quadrupole, crystal electric field, electron spin fluctuations) governing the temperature dependence of the spin-lattice relaxation time T1 in pure and doped samples at different temperature ranges are considered. Unlike T1, the spin-spin relaxation time T2 for pure and Nd-doped samples only weakly depended on temperature over the whole temperature range studied. Doping BGO with paramagnetic atoms strongly elongated T2, the elongation being also observed under the influence of weak external magnetic fields. The magnetization of doped BGO crystals vs. magnetic field and temperature was measured using a SQUID magnetometer. The temperature behavior of magnetic susceptibility for the Nd-doped BGO crystal evidenced for the presence of the crystal electric field effects. The curves of magnetization vs. magnetic field measured for the Gd-doped BGO crystal under field cooling and zero-field cooling conditions were markedly different, although this difference was less pronounced than that for the α-Bi2O3 crystal [1]. References [1] E.A. Kravchenko, V.G. Orlov, and M.P. Shlykov, Russian Chem. Rev. 75, 77 (2006). [2] E.A. Kravchenko, Yu.F. Kargin, V.G. Orlov, T. Okuda, K. Yamada, JMMM, 224, 249 (2001). [3] E.A. Kravchenko, V.G. Orlov, V.G. Morgunov, M.P. Shlykov, Hyperfine Interact. 180, 437 (2007). [4] E.A. Kravchenko, V.G. Morgunov, V.G. Orlov, Yu.F. Kargin, JETP Letters. 86, 390 (2007).Speaker: Prof. Valery Orlov (Russian Research Center "Kurchatov Institute", Moscow 123182, Russia)
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15:40
COFFEE BREAK 500/1-001 - Main Auditorium
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POSTER SESSION MEZANINE
MEZANINE
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CONFERENCE BANQUET CRUISE ON LEMAN LAKE
CRUISE ON LEMAN LAKE
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Convener: Helena Maria PETRILLI
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Calculations of Hyperfine parameters in solids based on DFT and using WIEN2kI will review briefly the underlying concepts of electronic structure calculations in solids and more specifically describe density functional theory and the APW+lo method as implemented in the WIEN2k code [1]. Special emphasis will be given to explain the calculations of isomer shifts, magnetic hyperfine fields and electric field gradients (EFG) and in particular I’ll discuss how we can interpret the results and what we can learn from a particular hyperfine parameter. For the case of several fluoro-aluminates I’ll demonstrate the strong dependency of the EFG (and even more of the asymmetry parameter on the exact atomic positions, which makes it mandatory to optimize the internal coordinates since often the experimentally determined positions are not accurate enough [2]. Mössbauer spectroscopy is also a very valuable tool to study matter under extreme conditions and recently [3] we could explain the large change of the EFG with pressure in (Mg,Fe)SiO3, a very important material in the lower mantle of the earth. Finally I’ll discuss EFGs, isomer shifts and hyperfine fields in YBaFe2O5 (Fig.1), a material which exhibits a Verwey transition between a charge-ordered and valence-mixed state [4] with temperature. During this transition the crystal structure, the magnetic order, the charge state and the hyperfine parameters change dramatically.Speaker: Peter Blaha (TU Vienna)
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Electron penetration into the nucleus and its effect on the quadrupole interactionA series expansion of the interaction between a nucleus and its surrounding electron distribution provides terms that are well-known in the study of hyperfine interactions: the familiar quadrupole interaction and the less familiar hexadecapole interaction. If the penetration of electrons into the nucleus is taken into account, various corrections to these multipole interactions appear. The best known correction is a scalar term related to the isotope shift and the isomer shift. This contribution discusses a related tensor correction, which modifies the quadrupole interaction if electrons penetrate the nucleus: the quadrupole shift. We describe the mathematical formalism and provide first-principles calculations of the quadrupole shift for a large set of solids. Fully relativistic calculations that explicitly take a finite nucleus into account turn out to be mandatory. Our analysis shows that the quadrupole shift becomes appreciably large for heavy elements. Implications for experimental high-precision studies of quadrupole interactions and quadrupole moment ratios are discussed. This contribution brings alive the results that are reported in Ref. [1], updated with very recent experimental follow-up work [2]. References [1] K. Koch, K. Koepernik, D. Van Neck, H. Rosner, S. Cottenier, Physical Review A 81 (2010) 032507, [2] D. Dewald, J. Grabow, in preparationSpeakers: Ms Katrin Koch (Instituut voor Kern- en Stralingsfysica, KULeuven, Max Planck Institute for Chemical Physics of Solids, Dresden, Germany), Mr Stefaan Cottenier (Center for Molecular Modeling -- Universiteit Gent)
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Quadrupole interaction in the solid halogens - a new (not final) lookThe nuclear quadrupole interaction in the molecular crystals of chlorine, bromine and iodine has been studied very early after the introduction of the NQR method. One should thus believe that precise experimental results are available. It will be argued here that for Cl2 and Br2 this is not the case at all. Obviously several attempts on interpreting the existing data have been made. Actually already in the first theoretical analysis [1] doubts on the results for solid Br have been raised, but afterwards ignored. In a pioneering work really free from parameters the EFG for solid Cl2, Br2 and I2 was calculated with the density functional method FLAPW [2]. The comparison of the calculated asymmetry parameters with experiment was inconclusive, however. The intermolecular interaction that creates also will have an influence on the interaction frequency when compared to the free molecule value0. Since precise experimental data for this shift /0 are available, here an attempt is described to treat both effects on the same footing. The same method previously used to determine the halogen nuclear quadrupole moments [3] was therefore applied to the free halogen molecules and the solids. It is obvious that the FLAPW calculations overestimate the frequency shift by a factor of about 2 in all three cases. It is thus extremely likely that the same holds also for . Under the assumption that the degree of overestimation for /0 and is the same, “corrected” values for may be obtained. This results in a perfect agreement with the precisely known value for I2. It could be demonstrated with FLAPW calculations of expanded unit cells that the effects of the intermolecular interaction on /0 and are correlated. From these calculations also for the first time a realistic theoretical result for the sublimation enthalpies is obtained. It may be hoped that the interpretation presented here will act as a stimulus for new experiments and theoretical treatments that can describe the intermolecular interaction better than FLAPW. The results are summarized in Table 1:Speaker: Heinz Haas (Instituto Tecnologico et Nuclear ITN)
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A-priori calculations of hyperfine interactions in highly ionized atoms: g-factor measurements of pico-second states populated in nuclear reactions.report of new calculation of hyperfine interactions in complex ions applied to g-factor measurementsSpeaker: Nicholas Stone (Oxford University/University of Tennessee)
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COFFEE BREAK 500/1-001 - Main Auditorium
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THEORY 500/1-001 - Main Auditorium
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Electric field gradient calculations by quantum chemical methodsThe electric field gradient, which from the point of view of the given nucleus is a measure of the inhomogeneity of the external electric field of all other charges, is a molecular property of the first order and can be determined from the knowledge of the electronic wave function and positions of nuclei. Since for accurate calculations we have to use highly sophisticated electron correlation approximations like the Coupled Cluster Singles and Doubles with non-iterative Triples CCSD(T) method, which does not fulfill the Hellmann-Fyenman theorem, and therefore we are forced to use so-called derivatives methods instead of calculating the expectation value of the given operator. Inclusion of relativistic effects in calculation of electric field gradients is inevitable [1]. If one– or two–component relativistic methods (e.g. DKH, IOTC) are exploited, the usual method of computing, which is just a counterpart of the nonrelativistic scheme leads to the change of picture effect [2] manifested by significant inaccuracies of the calculated property values. Different techniques how to avoid the change of picture effect will be discussed [3-5]. The combination of experimental nuclear quadrupole coupling constant obtained from microwave spectra and theoretical electric field gradient provides currently the best source of nuclear quadrupole moment values, at least for light elements. A series of such determinations of nuclear quadrupole moments will be presented [6-11]. References: [1] M. Iliaš, V. Kellö, M. Urban; Acta Phys. Slovaca, in press. [2] V. Kellö, A. J. Sadlej; Int. J. Quantum Chem., 68, 159 (1998). [3] M. Pernpointner, M. Seth, P. Schwerdtfeger; J. Chem. Phys., 108, 6722 (1998). [4] V. Kellö, A. J. Sadlej; J. Chem. Phys., 112, 522 (2000). [5] V. Kellö, A. J. Sadlej; J. Chem. Phys., 120, 9424 (2004). [6] V. Kellö, A. J. Sadlej, P. Pyykkö, D. Sundholm, M. Tokman; Chem. Phys. Letters, 304, 414 (1999). [7] V. Kellö, A. J. Sadlej; Mol. Phys., 96, 275 (1999). [8] V. Kellö, P. Pyykkö, A. J. Sadlej, P. Schwerdtfeger, J. Thyssen; Chem. Phys. Letters, 318, 222 (2000). [9] J. Bierroń, P. Pyykkö, D. Sundholm, V. Kellö, A. J. Sadlej; Phys. Rev A, 64, 052507 (2001). [10] L. Demovič, V. Kellö, A. J. Sadlej, S. A. Cooke; J. Chem. Phys., 124, 184308 (2006). [11] V. Kellö, A. J. Sadlej; Collect. Czech. Chem. Commun. 72, 64 (2007).Speaker: Prof. Vladimir Kelloe (Comenius University Bratislava)
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SEMICONDUCTORS, METALS AND INSULATORS 500/1-001 - Main AuditoriumConvener: Guido LANGOUCHE
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CONCLUSION 500/1-001 - Main Auditorium
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