Magnetic behaviour of Ni0.4Zn0.6Co0.1Fe1.9O4 spinel nano-ferrite

Nanoparticles of the spinel ferrite Ni0.4Zn0.6Co0.1Fe1.9O4 , have been synthesized by a co-precipitation method. The x-ray diffraction patterns of the particles confirmed the formation of single-phase cubic spinel structure. The Langevin function fitting on M-H data at 300K gives a log-normal particle size distribution with median diameter of 59.6 nm and standard deviation of 0.6. The isothermal dc magnetization studies have been performed using the superconducting quantum interface device and vibrating sample magnetometer in the temperature range of 5-300K. These measurements show that the sample is superparamagnetic above the blocking temperature T-B similar to 253K when an external magnetic field of 20 Oe is applied. The reduction in saturation magnetization in case of nanoparticles may be attributed to the fact that magnetic moments in the surface layers outside the core are in the state of frozen disorder. A doublet observed in the Mossbauer study also confirms the superparamagnetic behavior and nanocrystalline formation. (C) 2012 American Institute of Physics. [doi:10.1063/1.3670606]