Surface magnetic properties and domains observation in as-quenched and annealed FeNbB ribbons

The longitudinal magneto-optical Kerr effect (MOKE) combined with the magneto-optical microscopy is used to investigate the surface magnetic anisotropy and the domain behavior in as-quenched (AQ) and strain-annealed (SA) FeNbB ribbons. X-ray diffraction, conversion electron Moessbauer spectroscopy (CEMS), and scanning electron microscopy (SEM) confirmed the existence of approximately 1.3μm thick magnetically harder layer on the ribbon air side, consisting of crystallites embedded in an amorphous matrix. The underneath bulk phase is amorphous and magnetically soft. Residual anisotropies and the domain patterns (wide in-plane domains with 180 deg. walls and narrow fingerprint domains) corresponding to amorphous phase are mainly caused by the internal stresses originating from the rapid quenching process. In the surface crystalline phase they are gradually overlapped by strip domains with magnetization directions almost perpendicular to the ribbon axis. The anisotropy changes caused by additional annealing and straining of the samples are shown and discussed in detail.