Depth-sensitive characterization of surface magnetic properties of as-quenched FeNbB ribbons

The longitudinal magneto-optical Kerr effect (MOKE) is used to study the surface magnetic properties of as-quenched FeNbB ribbons. MOKE surface hysteresis loops measured from both ribbon sides confirm different magnetic behavior. Wheel ribbon side shows heterogeneous (crystalline/amorphous) properties, thickness of crystalline phase (about 3 nm) was established by comparing the measured magneto-optical angles of Kerr rotation and ellipticity at different incident angles with the theoretical model. Effective crystalline phase observed at shiny ribbon side is harder (coercive field about 40 Oe) than that on wheel side and penetrates deeper into the material volume. Its thickness 1.3 imagem estimated from the weight reduction of the ribbon during surface etching is in good agreement with cross-section image obtained using the scanning electron microscopy (SEM). The sources of magnetoelastic anisotropy were identified in the bulk as well as on the ribbon surface using the magneto-optical Kerr microscopy.