Strain induced magnetic anisotropy and 3d7 ions effect in CoFe2O4 nanoplatelets

Cobalt ferrite (CoFe2O4) magnetic nanoplatelets were synthesized by hydrothermal method at 120 °C (H120) and 180 °C (H180) respectively. The formation of inverse spinel cobalt ferrite was confirmed by X- ray diffraction pattern (XRD) and Transmission electron microscopy (TEM). The X-ray diffraction studies shows the linear variation of microstrain with inverse crystallite size. The compressive microstrain of 0.024 and 0.016 was estimated for CoFe2O4 samples H120 and H180 respectively using Williamson-Hall (W-H) plot analysis assuming uniform deformation model. The valence state of metal ions and single phase formation single domain CoFe2O4 was confirmed by X-ray photoemission spectroscopy (XPS) and Raman spectroscopy. X-ray photoemission spectra (XPS) exhibit Fe 2p3/2 peak and Co 2p3/2 peaks in both samples composed of two peaks corresponding to octahedral sites and tetrahedral sites. The strain induced magnetic anisotropy is estimated on basis of strain measured by W-H plot at 300 K. The contribution of the Co2+ ions on octahedral sites of both samples of CoFe2O4 is assigned to the magnetostriction ions in cubic structure of cobalt ferrite by assuming ground state. The magnetic ions with 3d7 transition in CoFe2O4 lattice introduced the local magnetostriction through spin-orbit-lattice interaction with distorted cubic crystal field.