We present a time-resolved study of the magnetization dynamics in a microstructured Cr$|$Heusler$|$Pt waveguide driven by the Spin-Hall-Effect and the Spin-Transfer-Torque effect via short current pulses. In particular, we focus on the determination of the threshold current at which the spin-wave damping is compensated. We have developed a novel method based on the temporal evolution of the magnon density at the beginning of an applied current pulse at which the magnon density deviates from the thermal level. Since this method does not depend on the signal-to-noise ratio, it allows for a robust and reliable determination of the threshold current which is important for the characterization of any future application based on the Spin-Transfer-Torque effect.
We investigate the amplification of externally excited spin-waves via the spin-transfer-torque (STT) effect in combination with the spin-Hall effect (SHE) resulting from short current pulses. In the case of overcompensation of the spin-wave damping, a strong nonlinear shift of the spin-wave frequency spectrum occurs. In particular, this shift limits spin-wave amplification from the SHE-STT effect. However, it allows for the realization of a spin-wave switch. At the corresponding working point, efficient spin-wave excitation is possible only in the presence of the SHE-STT effect with a spin-wave intensity that is a factor of 20 larger than in the absence of the SHE-STT effect.
We prove that groups acting geometrically on delta-quasiconvex spaces contain no essential Baumslag-Solitar quotients as subgroups. This implies that they are translation discrete, meaning that the translation numbers of their nontorsion elements are bounded away from zero.