Chitosan coating by mechanical milling of MnFe2O4 and Mn0.5Co0.5Fe2O4: Effect of milling

Manganese ferrite (MnFe2O4) and manganese-cobalt ferrite (Mn0.5Co0.5Fe2O4) fine powders were produced by glycol-thermal technique. Fine powders were then milled with chitosan for different times ranging from 5 hours to 60 hours. XRD patterns of the as-prepared and milled oxides confirm cubic phase structure with an average crystallite size of 11 nm. The observed values of lattice parameter decrease with milling due to the inversion of cations induced by milling. TEM results reveal nanoparticles with spherical shape and average particle sizes correlating to XRD data. No aggregation of particles was observed after milling suggesting effective chitosan coating. Magnetization studies performed at room temperature in fields up to 14 kOe revealed the superparamagnetic nature of both naked and coated nanoparticles with spontaneous and saturation magnetizations decreasing with milling. Larger coercive fields observed in Mn-Co oxides were attributed to higher magnetic anisotropy associated with Co ions. A reduction of coercive field due to milling duration was observed. Fe-57 Mossbauer spectra of Mn0.5Co0.5Fe2O4 samples show ordered magnetic states, while paramagnetic nature is revealed in MnFe2O4 samples. Hence, current results suggest that chitosan coating can be successfully achieved through mechanical milling resulting in nanoparticles with potential for biomedical applications. The differences in the magnetic properties of the samples are discussed based on Stoner-Wohlfarth theory.