Anisotropy and domain state dependent enhancement of single domain ferrimagnetism in cobalt substituted Ni-Zn ferrites

Nanocrystalline Co substituted Ni-Zn ferrites with the general formula CoxNi0.6-xZn0.4Fe2O4 (x = 0.0 to 0.6) were prepared by a precursor combustion method. Average crystallite size, as estimated by using a Scherrer method and the particle size obtained from transmission electron microscopy (TEM) techniques, was found to be in the range of 10-30 nm. EDX and XRD analysis confirms the presence of Co, Ni, Zn, Fe and oxygen and the desired phases in the prepared nanoparticles. Selective area electron diffraction ( SAED) analysis confirms the crystalline nature of the prepared nanoparticles. It is observed that Co substitution has a pronounced effect on the magnetic properties such as M-R, M-S and H-C and also on the Curie temperature (TC), which is found to decrease from 420 degrees C for non-substituted Ni- Zn ferrites to 325 degrees C for the highest substitution of x = 0.6. These effects are assigned to the higher magnetocrystalline anisotropy of Co than Ni and to the size dependent existence of single domain-superparamagnetic particles distribution. Comparatively, the dominant existence of single domain particles with Co substitution over superparamagnetic particles in non- substituted nickel zinc ferrites is extensively investigated in this article.