Influence of oxygen vacancies on the magnetic properties of ZnFe2O4

K. L. SALCEDO RODRÍGUEZ; M. HOFFMANN; J. J. MELO QUINTERO; G. PASQUEVICH; P. MENDOZA ZÉLIS; L. ERRICO; S. J. STEWART; W. HERGERT; C. E. RODRÍGUEZ TORRES

Encuentro; Deutsche Physikalische Gesellschaft; 2015

To investigate the influence of oxygen vacancies in the ferromagnetism observed in Zn-ferrites systems[1] we have performed an experimental and theoretical study on bulk ZnFe2O4 powders submitted subjected to thermal treatments up to 600oC under low oxygen pressure atmosphere. The effect of vacancies on the structural and magnetic properties of ZnFe2O4 have also been studied by DFT-based ab initio calculations. The x-ray diffraction patterns indicate that all samples consist of single-phase ferrite The results of magnetic measurements show the coexistence of ferromagnetic-like and paramagnetic components. Further, both the saturation magnetization and paramagnetic susceptibility progressively decrease as the ferrite is annealed up to 400oC. For higher annealing temperatures both magnitudes increase reaching the maximum values at 600oC. Mossbauer spectroscopy measurements performed at room temperature show a unique doublet for all samples. Changes on the hyperfine parameters values are only detected for samples annealed at temperatures higher than 400oC. Theoretical calculations using the full potential augmented plane waves plus local orbitals method (FP-APW+lo) were performed also, considering different approximations of exchange correlation potential (GGA, GGA +U)considering the normal, inverted and oxygen-deficient ferrites. The comparison between the experimental and calculated hyperfine parameters indicated the possibility of a reversal process of inversion to lower temperatures (330oC to 380oC, approx.) and vacancies formation process at the higher temperatures (400oC to 600oC) is occurring. Then, we conclude that the increases in saturation magnetization and paramagnetic susceptibility observed in the samples annealed at temperatures higher than (400oC) is due to the oxygen vacancies formation.