HFI/NQI 2010

Lattice Location and Diffusion of Interstitial Fe in MgO

Not scheduled

500/1-001 - Main Auditorium (CERN)

POSTER Lattice Dynamics, Ion-Solid Interaction

Speaker

Torben Esmann Mølholt (University of Iceland)

Description

T. 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, A. Svane3, 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. 3d-metal doped MgO has been suggested as a model system for dilute magnetic semi-conductors [1]. However, the physics of 3d-metal impurities is poorly understood [2,3]. We present an 57Fe emission Mössbauer study on dilute Fe impurities in single-crystalline MgO (77 – 649 K) following implantation of radioactive 57Mn+ (T½ = 85.4 s) at the ISOLDE facility at CERN. Due to the recoil imparted on the daughter 57*Fe atoms in the β--decay ( 40 keV) interstitial 57mFe atoms are created. Figure 1 shows the central part of the measured Mössbauer spectra at different temperatures (see [3] for details). At low temperatures the central part is dominated by an asymmetric quadrupole doublet (red) assigned to Fe in heavily damaged/amorphous regions caused by the implantation. At high temperatures the spectra are dominated by a single line (pink) assigned to Fe2+ on substitutional Mg sites. During the fitting procedure a single line had to be introduced, the line of interest her, which is attributed to interstitial Fe (blue). The wings of the spectra show a magnetic sextet structure assigned slowly relaxating Fe3+ (green); more details of this component are described elsewhere [4]. The interstitial line exhibits a broadening at elevated temperatures which can be associated with diffusional jumps of interstitial Fe on the time-scale of the decay lifetime of the Mössbauer state (140 ns). A diffusion coefficient of D = 1.4(3)×10-9 cm2/s at 300 K is thus obtained. This value is orders of magnitude higher than suggested for vacancy-assisted Fe diffusion in MgO [5]. However, there is experimental evidence for a fast diffusion of 3d-metal impurities in MgO [2,3]. The Mössbauer parametres of the interstitial Fe are in good agreement with theoretical calculations for interstitial Fe atoms is located at the face of the rock salt fcc MgO crystal structure. References [1] J. Narayan, N. Sudhakar, D. K. Pandya, D. K. Avasthi, A. I. Smirnov, Appl. Phys. Lett., 93, 082507 (2008). [2] M. Lu, C. Lupu, J. W. Rabalais, Appl. Phys. Lett., 81, 5033 (2002). [3] R. A. Weeks, J Gastineau, E. Sonder, Phys. Status Solidi (a) 61, 265. [4] T. E. Mølholt et al. (2010) this conference. [5] M. J. L. Sangster, A. M. Stoneham, J. Phys., C, 17, 6093 (1984).