Manipulation of the gyrotropic mode frequency and band structure in an FM / AFM disk via vortex imprinting

Abstract

We experimentally investigate the magnetic gyrotropic mode in a system of vortex ferromagnetic (FM) nanooscillator exchange coupled to an antiferromagnetic (AFM) layer. The micron-sized disks formed from the Ni80Fe20(12 nm) / Ir80Mn20 (5 nm) FM/AFM heterostructure are prepared so that the vortex magnetic state is imprinted into the AFM layer. We apply a magnetic resonance force microscopy (MRFM) method to locally study magnetic oscillations in single FM/AFM disks. We show that the gyrotropic mode frequency is significantly (approximately 4 times) shifted to the high frequency compared to similar structure consisting of a single ferromagnetic disk. Upon applying an in-plane magnetic field, we observe a strong peak at a double frequency which was previously predicted in theory. This is governed by the fact that vortex dynamics is strongly nonlinear in a noncentrosymmetric system under investigation.