Role of Shell Thickness and Applied Field on The Magnetic Anisotropy and Temperature Dependence of Coercivity in Fe3O4 /γ-Fe2O3 Core/shell Nanoparticles
We report on the effect of shell thickness and the magnetic field on the effective magnetic anisotropy, K eff and on the temperature dependence of coercivity, H C (T) in Fe3O4/γ-Fe2O3 core/shell nanoparticles of fixed diameter (8 nm) and several shell thicknesses (1, 3 and 5 nm). The particles are synthesized by the usual co-precipitation method. The phase and the morphology of the sample are characterized by X-ray diffraction and transmission electron microscopy. The morphology of the nanoparticles is confirmed by high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED). The magnetic measurements are carried out using a SQUID in the temperature range of 2 K to 300 K both under zero field-cooling (ZFC) and fieldcooling (FC) protocols with field-cooling values, H FC of 0.5 T, 1 T, 2 T and 3 T. H C(T) in the samples is found to significantly deviate from the original Kneller's law. These deviations are attributed to modifications of the interfacial magnetic anisotropy that resulted from variations in the interfacial spin-glass regions with shell thickness and field-cooling. K eff is calculated using two methods based on the magnetization measurements. In the first method we used the H C(T) curves obtained from the ZFC and FC magnetization versus magnetic field M–H hysteresis loops. In the second method the ZFC magnetization versus temperature (M–T) measurements are used at several applied magnetic fields. We compared and discussed the different results of K eff obtained by these two methods.
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Document Type: Research Article
Publication date: April 1, 2019
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