A new phenomenon on the surface of FINEMET alloy

Abstract

This paper is devoted to the analysis of quadratic magneto-optical effects (QMOKE) newly observed at the surface of FINEMET-type Fe73.5Si13.5Nb3Cu1B9 ribbons annealed at temperatures of 733 K and 743 K. A strongly inhomogeneous surface microstructure detected by grazing incident X-ray diffraction (GIXRD), scanning (SEM) and transmission (TEM) electron microscopy is responsible for amplitude and sign changes of the QMOKE in different sample places. Signals in saturation determined by an 8-directional method confirm the prevailing influence of M L M T contributions at some places of a surface and of M2L−M2T at other ones, where M L and M T are in-plane longitudinal and transversal magnetization components. This behavior is explained by random orientation of nanocrystals and/or clusters of the nanometer size (typically units of nm) in the surface layers. The maximal QMOKE magnitude in saturation reaches at some places as much as 0.2 mrad, which is approximately three times lower than the highest contribution observed in Co2FeSi Heusler compounds.