Microstructural and magnetic behavior of mixed Ni–Zn–Co and Ni–Zn–Mn ferrites

Co/Mn substituted Ni–Zn ferrite nanoparticles were prepared by the sol–gel autocombustion method using metal nitrates in citric acid matrix to estimate the influence of substitutions on the microstructural and magnetic properties of the Ni–Zn ferrites. The synthesized powders were pressed into desired shapes and sintered at 1200 °C for 4 h in air atmosphere. X-ray diffraction analyses of the samples confirm single phase cubic spinel structures. Scanning electron micrographs of the materials reveal that the substitutions resulted in fine grained intragranular pore free microstructures. Initial permeability of the substituted ferrites exhibits stable frequency response up to 8–10 MHz beyond which it exhibits a sharp resonance character while the relative loss factor has been found to be quite low up to this frequency. The results are explained in terms of the compositional, microstructural and anisotropic modifications brought about by the Co or Mn substitutions in these materials.