LINEAR AND QUADRATIC MAGNETOOPTICAL MEASUREMENTS OF THE SPIN REORIENTATION IN EPITAXIAL FE FILMS ON MGO

We have undertaken a detailed study by magneto-optical techniques of i n-plane magnetization reversal behaviour in epitaxial Fe films grown b y MBE on (1 0 0) oriented MgO substrate. We measure M-H loops for both orthogonal in-plane magnetization components M-l (component parallel to the magnetic field) and M-t (component perpendicular to the field) and for various orientations of the magnetic field with respect to the crystalline axis. These measurements show the classical four-fold cub ic anisotropy for large Fe film thickness and confirm the appearance o f weak uniaxial in-plane anisotropy superimposed for thinner films (t = 20 Angstrom). We have demonstrated the appearance of strong asymmetr ical hysteresis loop for p-polarized incident light. We explain this b ehaviour as the mixing of transverse magnetization contribution to the longitudinal magnetization measurements on the basis of quadratic mag neto-optical effects. The calculation of these effects based on eigenm ode propagation in anisotropic layered media are developed by includin g the second-order magneto-optical terms in the permittivity tensor ch aracteristic of a cubic crystal. The second-order reflection coefficie nts are discussed in the case of the normal incidence of the laser bea m and for the magnetic field along the hard axis of the Fe film.