Depth sensitivity of magneto-optic Kerr effect on FeNbB amorphous ribbons

FeNbB amorphous ribbons are promising soft magnetic materials with adjustable surface magnetic properties. Field-annealing is applied to control nano-crystallized surface magnetic films, which can be monitored by using magneto-optical techniques. In this paper we analyze depth sensitivity of magneto-optic methods and investigate the surface magnetic properties of amorphous ribbons. Magneto-optic response and depth sensitivity is modeled using 4 x 4 matrix formalism of light propagation in anisotropic multilayers. Optical and magneto-optical properties of near surface nano-crystallized phases differ from those of deeper bulk material. The complex longitudinal magneto-optic Kerr effect is measured for s- and p-polarized incident light. Both magneto-optical angles: the Kerr rotation and Kerr ellipticity are analyzed. Separation of magneto-optic contributions from different layers is obtained using different phase sensitive and penetration depth of the complex magneto-optic measurements. For these measurements we use magneto-optic vector magnetometry based on differential intensity between two polarization states.