The observation of non-homogeneous FMR modes in multilayer Fe/Cr structures

The spectrum of excitations in [Fe/Cr] n structures with a non-collinear magnetic ordering was studied by means of the FMR technique. The measurements were carried out at room temperature in the frequency range of 9.5–37 GHz with both static and microwave magnetic fields lying in the film plane. Along with the acoustic FMR mode several additional modes were observed in the longitudinal pumping configuration. The resonance spectrum of an infinite magnetic superlattice was calculated analytically on the basis of the biquadratic exchange coupling model. Both cases were considered: external magnetic field H parallel and perpendicular to the film plane. It was shown that the observed additional FMR modes correspond to the excitation of standing spin waves with wave vectors perpendicular to the superlattice plane.