The effect of cationic disorder on low temperature magnetic properties of MnZn ferrite nanoparticles

Bulk MnZn spinel-ferrite compacts are commonly used in the medium range frequency applications, while their nanoparticle (NP) counter parts are envisaged for biomedical applications like drug delivery, magnetic hyperthermia treatments and magnetic resonance imaging. It is now established that the magnetic properties of NPs depend on the method of synthesis, particle size, cat-ion distribution and composition. In bulk ferrites the competition between the two sub-lattice magnetization generates interesting M-T curves while in NPs undergo further changes as a function of temperature due to superparamagnetic (SPM) and surface spin effects. Although the SPM limit of the particles is reported to be ~20 nm, it is observed that the blocking temperature (T_B) increases with Mn concentration. However, when NPs are heat treated at higher temperatures the T_B increased for Zn-ferrite while it is decreased for Silica-coated Zn-ferrite NPs. In this work we investigate low temperature magnetic properties of Mn_xZn_1-xFe₂O₄ (x=0.0 and 0.6) ferrites NPs in comparison with their bulk counterpart to obtain deeper understanding into the nature of transition temperature. Further we delve upon the origin of the magnetic transition observed in these systems.