TEMPERATURE DEPENDENCE OF MAGNETIC PROPERTIES OF SINGLE CRYSTALLINE Fe_3O_4 THIN FILMS EPITAXIALLY GROWN ON MgO

摘要

Single crystalline Fe_3O_4 thin film of 110 angstrom in thickness grown on MgO (100) substrate have been investigated by Electron Spin Resonance technique as a function of temperature between 3 and 300K. Experimental spectra taken at different temperatures were analysed by classical Spin Wave Resonance (SWR) technique for different orientations of sample for both in-plane and out-of plane geometry. SWR spectra exhibit unidirectional character upon cooling the sample in the presence of external field, Hc. A strong unidirectional (Exchange) anisotropy field as evidenced from a shift of the resonance field for r-FC case relative to that for n-FC case at low temperature. Using a field-induced unidirectional exchange and bulk anisotropy, with the usual magneto-crystalline cubic anisotropy energy, we have simulated the experimental spectra and angular dependence of resonance field and deduced anisotropy and other magnetic parameters as a function of temperature. Verwey transition for thin film case was found to shift down to around 90 K from 120 K for bulk sample of the same compound.