Surface magnetic behavior and microstructures of ferromagnetic (Co77Si13.5B9.5)90Fe7Nb3 ribbons

Different kinds of magnetic anisotropies have been induced during the nanocrystallization process of Co-rich amorphous ferromagnetic (Finemet) ribbons ((Co 77 Si 13.5 B 9.5 ) 90 Fe 7 Nb 3 ) using diverse procedures like the application of a constant stress or an axial magnetic field during the annealing process. Magnetization measurements of the samples by a fluxmetric method in quasistatic conditions have evidenced the anisotropy of the treated Finemet samples. The main goal of this work has been the structural and microstructural analysis of the treated ribbons using X-ray Diffraction and Atomic Force Microscopy (AFM), detecting substantial differences in the crystallization state and grain size of the samples depending on the treatment that was carried out. Moreover, AFM measurements revealed in all the treated samples a strong nanocrystallisation of the surface without evidences of amorphous matrix, which contrast with Transmission Electron Microscopy measurements that have shown a high content of amorphous phase in the bulk of the ribbons. Additionally, magneto-optical Kerr effect measurements have been performed with the aim to elucidate the complex magnetic behavior that is expected for the surface of the ribbons, measuring surface hysteresis loops that show much higher coercive field values than in the bulk.