Magnetic Properties of Mn-Substituted Zn–Mg- and Zn–Co-Nanosized Compounds

Mn-substituted Zn–Mg and Zn–Co with chemical formula Mn0.3Mg0.2TM0.5Fe2O4 (TM = Zn or Co) fine powders have been synthesized by glycol-thermal process. XRD results reveal the formation of a cubic phase without any impurity phases. TEM images show nearly spherical particles with fairly distributed particles with an average crystallite size of about 14 nm. 57Fe Mossbauer spectral studies show well-resolved magnetic splitting in the Mn–Mg–Co oxide due to stronger superexchange interactions. FC and ZFC magnetization data revealed the superparamagnetic nature of the compounds investigated. Mn–Mg–Zn nanoparticles are blocked at about 206 K while the maximum blocking temperature of Mn–Mg–Co-nanosized oxide is above 300 K. These differences were discussed on the basis of Stoner-Wohlfath relation TB = KV /25kB.