Tuning magnetization, blocking temperature, cation distribution of nanosized Co0.2Zn0.8Fe2O4 by mechanical activation

Abstract

The study on structural, microstructural, magnetic, and hyperfine properties of nanosized Co0.2Zn0.8Fe2O4 having particle size ∼18 nm (CZM) synthesized by high energy ball milling of Co0.2Zn0.8Fe2O4 nanoparticles of size ∼20 nm (CZ) produced by flow rate controlled coprecipitation method has revealed that the inclusion of strain induced anisotropy produced by mechanical treatment and escalation of oxygen mediated intersublattice exchange interaction of spinel ferrites by tuning cation distribution properly, can improve the magnetic quality of nanosized ferrites significantly. This upshot will be of immense help in promoting the technological application of nanostructured ferrites. The Rietveld refinement of powder x-ray diffraction pattern and the analysis of transmission electron micrographs, energy dispersive x-ray spectrum, and FTIR spectrum of the sample have confirmed that CZM is single phase cubic nanometric spinel ferrite of Fd3¯m symmetry and it possesses large microstrain within its crystal lattice. The dc magnetic and Mössbauer spectroscopic studies together with indicate that the particles in the sample are composed of ferrimagnetically aligned core and spin-glass like shell and the system behaves superparamagnetically at 300 K. The saturation magnetization (44 and 87 emu g−1 at 300 and 10 K) and hyperfine field of the sample are substantially higher than its counterparts reported earlier. In spite of its lower size compared to CZ, the blocking temperature (∼220 K) of CZM is higher than that of CZ (70 K) and also that of its counterparts synthesized by chemical methods. The strengthening of the intersublattice A-O-B superexchange interaction because of migration of Fe3+ ions from octahedral [B] to tetrahedral (A) sites in lieu of the relocation of Zn2+ among (A) and [B] sites helps in enhancement of magnetization and hyperfine field of CZM. The giant coercivity (HC ∼ 5600 Oe at 10 K) of CZM is accounted by the presence of spin glass like surface layer in the sample. Moreover, the system exhibits striking memory effect which can be suitably utilized in storing binary bits (0, 1) through magnetic field change in the cooling cycle of magnetization versus temperature profile, and the stored binary coded number can be faithfully retrieved in the heating cycle.