Surface microstructure and magnetic behavior in FeSiB amorphous ribbons from magneto-optical Kerr effect

The magneto-optical Kerr effect (MOKE) completed by other surface sensitive methods as integral low-energy and conversion electron Mössbauer spectroscopy, scanning and transmission electron microscopy and by X-ray diffraction have been used with the aim to trace the surface microstructure and magnetic properties of FeSiB amorphous ribbons prepared by planar flow casting. The general composition of studied samples is Fe₈₀Si_xB_20−x, where x=4, 6, 8, 10 at.%.It is shown that MOKE used for magnetization, hysteresis loop, and domain structure determination is highly beneficial in a detection of both surface crystallization and local ordering of atoms into magnetically different clusters of amorphous structure. Moreover, a combination of blue and red laser with different penetration depths yields unique results concerning the surface anisotropy and depth sensitivity. In the case of samples with 4, 6, and 8 at.% Si MOKE detects two magnetically different phases diverging in coercivity values H_c, however, not varying with the sample composition. These phases have been identified by Mössbauer measurements as FeSi and FeB clusters. Their relationship changes with Si concentration. On the other hand, a strong increase in the surface H_c found for the sample with 10 at.% Si has indicated a nanocrystallization. It was confirmed by electron microscopy, Mössbauer and X-ray diffraction results. The size of nanocrystals has varied between 200 nm and 500 nm.