Effect of temperature on the magnetic characteristics of Ni0.5Co0.5Fe2O4 nanoparticles

Magnetic nanoparticles of Ni0.5Co0.5Fe2O4 (size: 18 ± 3 nm) have been synthesized by chemical co-precipitation route. Coercivity (HC) of the particles shows an increasing behavior with decreasing temperature and observes deviation from the Knellerʹs law for ferromagnetic nanostructures. Exchange bias effect (Hex) shows an exponential increase with decreasing temperatures followed by a sharp fall below ∼5 K. The saturation magnetization (Ms) follows modified Blochʹs law in the high temperature range (100–300 K), while below 100 K it shows a decreasing trend with decreasing temperature followed by slow increase in Ms at very low temperatures. Blocking behavior shows a decreasing trend in blocking temperature (Tb) of the system as the applied field in M(T) measurements is increased. The results have been discussed in terms of the variation of anisotropy with temperature, modified spin-wave theory predictions, interparticle interactions, and the presence of spin glass (SG) like phase at the surface of Ni0.5Co0.5Fe2O4 nanoparticles.