Mössbauer,infrared and X-ray studies for $Ni_{0.5}Zn_{0.5}Cr_xFe_{2-x}O_4$ ferrites

Özet

Spinel ferrites of the system $Ni_{0.5}Zn_{0.5}Cr_xFe_{2-x}O_4$, $0\leq x \leq 1$, have been studied via Mössbauer, IR and X-ray spectra. Mössbauer spectra of the samples showed broad six-line patterns and a central paramagnetic phase. The spectra have been analyzed to two magnetic patterns, A and B, and two quadrupole doublets, CA and CB. The patterns A and CA are assigned to $Fe^{3+}$ ions at the tetrahedral A-sites and the patterns B and CB to $Fe^{3+}$ and $Fe^{2+}$ ions at the octahedral B-sites. The deduced hyperfine interaction parameters; the isomer shifts, quadrupole splitting, outermost line widths, hyperfine magnetic fields and bulk magnetization were studied and discussed as functions of the $Fe^{3+}$ additions x. The cation distribution of the compounds was estimated using the site preference of elements and the area ratio of B- to A-sites. The broad magnetic pattern B has been fitted to several subpatterns. Using the obtained hyperfine parameters one could assign each of the B-subpatterns to a component depends on the number of nonmagnetic $Zn^{2+}$ ions as A-site nearest neighbours of the Fe ions at the B-sites. Five absorption bands were observed in the infrared spectra in the range between 1100 and 200 $cm^{-1}$. These bands are assigned to the $Fe^{3+}$ ions on A-sites; to $Fe^{3+}$ and $Cr^{3+}$ ions on B-sites; to divalent ions $Fe^{2+}$ and $Ni^{2+}$ and to the energy of the lattices. The existence of $Fe^2$ ions on the A- and B-sites has been confirmed. From X-ray analysis, the average, true, and theoretical lattice parameters, the theoretical and bulk densities, the porosity, the oxygen parameter and the ionic radii, bonds, edges and hopping lengths of the A- and B-sites have been calculated and discussed depending on the $Cr^{3+}$ ion content x. The dependency of the hyperfine field on the hopping length at the A- and B-sites has been studied and discussed.