Transformation of the gyrotropic mode spectrum of the FM / AFM disk via vortex imprinting
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 $Ni_{80}Fe_{20}$ (12 nm) / $Ir_{80}Mn_{20}$ (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 four times) shifted to the high frequency range compared to a 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 shows that nonlinearity in vortex dynamics is strongly enhanced in the FM/AFM system under investigation. Thus the magnetic imprinting technology reveals great potential for future application in high-frequency spintronic devices.