Microwave generation on geometrically constrained magnetic wall: Effect of twist angle

We studied the current-induced magnetization dynamics of geometrically constrained magnetic walls (GCMWs) with twist angles of 90-180°, in order to examine their possibility as microwave generators using the effects of the twist angles. We numerically solved the Landau-Lifshitz-Gilbert equation with a spin-transfer torque term and found that the magnetic structures of GCMWs with certain twist angles oscillate between the Bloch and Néel walls (OBN) with microwave frequency, even though the twist angle is not 180°. We also found the critical twist angle below which the oscillation of the magnetic structure is inhibited. We showed that the oscillation frequency shows a hysteresis when we vary the twist angle of a GCMW or the corresponding applied magnetic field. Then, we also discussed the microwave generation induced by the periodic-deformation dynamics of GCMWs in the OBN.