Angular dependence of microwave absorption in multilayer films

Microwave absorption measurements on a NiFe/Au/NiFe multilayer film were carried out at X-band (8.8-9.8 GHz). The angular dependence of microwave absorption, both in ferromagnetic resonance (FMR) and low-field microwave absorption (LFA), is investigated in two orientations. In both cases the film plane is orientated parallel to the AC field. In the longitudinal orientation, the film axis makes angles between 0° and 90° with the DC magnetic field (H_dc). In the transverse orientation, the film axis is always perpendicular to H_dc, marking angles between 0° to 90° with the axis of the induced transverse anisotropy. For the longitudinal orientation, FMR spectra suggested a compound absorption mode that can be interpreted as the combination of two different magnetic phases. Additionally, these measurements showed an increase in the resonance field as a function of the angle, which can be explained in terms of a contribution of shape anisotropy field (SAF). For this same orientation, the LFA spectra exhibited a compound antisymmetric shape around zero field with double peaks, which we associated with each one of the magnetic phases. The separation of these peaks increased as a function of the angle between the DC field and the multilayer film axis, suggesting also a contribution from SAF. In the transverse orientation, we observed an additional contribution of induced transverse anisotropy field (ITAF) in FMR measurements. The LFA measurements exhibited differences with the longitudinal orientation which are also associated with ITAF.