Study of hyperfine interactions in Fe3O4 and LaMnO3 oxides by perturbed gamma-gamma angular correlations

Nuclear techniques have been shown to be very useful tools to investigate fundamental properties in materials science and condensed matter physics. Among them the perturbed gamma-gamma angular correlation (PAC) spectroscopy has the advantage to be temperature independent e very sensitive to the crystalline array of constituent elements such as phase transitions, point defects, diffusion process, etc. PAC spectroscopy is based on the angular correlation between nuclear radiations emitted by radioactive nuclei, which is a well established method in nuclear spectroscopy. Perturbation occurs in this correlation by electromagnetic interactions external to the nucleus when it is inserted in a material, which can provide information on the electronic distribution of the neighborhood. In the present work two important materials were investigated by PAC spectroscopy using 111In, which decays to 111Cd by electron capture, as probe nuclei. Fe3O4 nanoparticles, a superparamagnetic oxide which have biomedical applications, were prepared by co-precipitation method and 111In (111Cd) was added to the samples by annealing of the pellet samples at different temperatures. LaMnO3, a ferromagnetic perovskite oxide, which has promising technological applications, was prepared by sol gel technique and 111In (111Cd) was introduced during preparation. Similar samples were prepared without radioactive 111In to be characterized by X-ray diffraction and results were analyzed by Rietveld method. Results showed that 111Cd nuclei substitutes Fe and La sites and, in the case of LaMnO3 the oxygen excess, which causes structural defects, are very small. (author)