Speaker
Mrs
Juliana Marques ramos
(Instituto de Pesquisas Energéticas e Nucleares / Helmholtz-Institut für Strahlen- und Kernphysik)
Description
Thin films and powder samples of intrinsic and transition metal doped titanium dioxide were investigated by an atomic resolution hyperfine nuclear technique in order to study the relation between defects and ferromagnetism. Complementarily, the crystalline structure, morphology and composition of the samples were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) characterization techniques. Magnetic properties were further investigated by magnetization measurements using a vibrating sample magnetometer (VSM). Hyperfine parameters were studied as a function of temperature by means of perturbed gamma-gamma angular correlation (PAC) spectroscopy using different probe nuclei 111In/111Cd, 181Hf/181Ta and 111mCd/111Cd. Thin films of 88-100 nm thickness were deposited by magnetic sputtering on Si (100) substrates, inducing the formation of the rutile phase. Doping of the films with Fe and Co was achieved by ion implantation and the powder samples were prepared by the Sol Gel Method. PAC measurements were carried out after implantation of 111In or 181Hf at the BONIS implanter in Bonn University, with and without magnetic field applied and after 111mCd at ISOLDE laboratory. After the initial measurements carried out as implanted, the samples were annealed at 600°C in vacuum or air, which allowed the permanence of defects caused by the implantation process and voluntarily lead to the formation of the Magnéli phases. PAC results show the presence of up to three site fractions for the probe nuclei depending on the heat treatment. One is assigned to the probe nuclei at the substitutional Ti sites and the other two can be assigned to defect sites, either near the doping ions or near shear planes, which gives rise to the observed magnetic interaction on the atomic scale PAC data and on a macroscopic scale magnetometry data. However, the most important result of this work was the correlation between the magnetic interactions and the observed rearrangement of the charges as a function of the temperature for all the three different probe elements nuclei. This means that the recombination of local charge carriers can be associated with the macroscopic observation of the hysteresis curves obtained by magnetometry, an effect that is enhanced with the decrease of the temperature.
Author
Mrs
Juliana Marques ramos
(Instituto de Pesquisas Energéticas e Nucleares / Helmholtz-Institut für Strahlen- und Kernphysik)
Co-authors
Dr
Artur Wilson Carbonari
(Instituto de Pesquisas Energéticas e Nucleares, University of São Paulo)
Dr
João Guilherme Martins Correia
(Instituto Tecnológico e Nuclear, Technical University of Lisboa / On-Line Isotope Mass Separator, European Council for Nuclear Research)
Dr
Rafael Sá de Freitas
(Instituto de Física, University of São Paulo)
Dr
Rajendra Narain Saxena
(Instituto de Pesquisas Energéticas e Nucleares, University of São Paulo)
Dr
Reiner Vianden
(Helmholtz-Institut für Strahlen- und Kernphysik, University of Bonn)
