Angular dependence of low-field microwave absorption in Co-rich amorphous alloys

Abstract

Microwave power absorption measurements at 9.4GHz (X-band) were carried out on as-cast amorphous ribbons of nominal composition Co66Fe4B12Si13Nb4Cu, prepared by melt spinning. The angular dependence of low-field absorption (LFA) was investigated from θ=0° to 180° in two orientations. In both cases the ribbon axis was orientated parallel to the DC magnetic field. In orientation 1, the ribbon plane was parallel to the AC microwave field. In orientation 2, it was perpendicular to the AC field. LFA spectra showed an antisymmetric shape (a minimum and a maximum), whose separation increased as a function of the angle between the DC field and the ribbon axis. A similar angular behavior was observed for the resonance field of the ferromagnetic resonance (FMR). For the orientation 1, the resonance field increased as a function of the angle, which can be explained in terms of the contribution of the shape anisotropy to the total anisotropy field. A similar behavior was observed in LFA, which suggests that the shape anisotropy field can be observed in the angular dependence of LFA. In the orientation 2, the observed changes occur within the plane associated with the induced anisotropy due to the rapid solidification process. The LFA signal is capable therefore to detect different contributions to the total anisotropy.