Effects of Zn-Cr-substitution on the structural and magnetic properties of Ni1−xZnxFe2−xCrxO4 ferrites

Cr and Zn-substituted nickel ferrites, general formula Ni1−xZnxFe2−xCrxO4 (x=0, 0.1, 0.3, 0.5, 0.7), were prepared using the sol-gel auto-combustion method. For precise analysis, the Ni1−xZnxFe2O4and NiFe2−xCrxO4 (x=0, 0.1, 0.3, 0.5, 0.7) samples were also checked individually. The effects of Cr and Zn doping on the structural, morphological, and magnetic properties of the samples were evaluated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometer (VSM). The full pattern fitting of Rietveld method using MAUD program was also applied to determine the exact coordinates of the atoms, unit cell dimensions, and ion occupancy. XRD measurement by Rietveld refinement confirmed the crystalline structure and phase purity of all the ferrites. SEM images showed that the particles were in the nanosize range. VSM results revealed that the values of MS in the NiFe2−xCrxO4 samples decreased and that HC had no regular behavior with increasing Cr content. The maximum value of HC=16 Oe was obtained for a Cr content of x=0.7. On the other hand, saturation magnetization values initially increased in both the Ni1−xZnxFe2−xCrxO4 and Ni1−xZnxFe2O4 samples, with changing the doping level up to x=0.3, while for further content, MS decreased. In addition, coercivity decreased with increasing doping level.