Our new work entitled ”Temperature and electric field effects on dynamic modes in spin current auto-oscillator”is published in Phys. Rev. B. [Phys. Rev. B 103, 144426(2021)]. In this work, we systematically study spectral characteristics of emission microwave signal by a spin current nano-oscillator (SCNO) based on TaOx/Py(3)/Pt(2) trilayers as a function of current, in-plane magnetic field angle, electrostatic gating, and temperature. The current dependence of spectral characteristics shows that such SCNO exhibits a single coherent oscillation mode at low currents, and then transfers into a multimode coexistence regime with several oscillation peaks, related to spatially separated oscillation regions, at high currents. The linewidth of these modes shows an exponential temperature dependence, indicating thermally activated mode transitions or mode hopping behavior among these spatially separated oscillation regions due to the mode coupling caused by strong thermal-magnon-mediated scattering rate at high temperatures. Additionally, electrostatic gating on oscillation frequency shows a temperature-independent behavior, but gets enhanced in the strongly nonlinear oscillation regime. The enhanced phenomenon is caused by a combination of nonlinear frequency redshift and driving current shift due to electric-field modulation of current-induced spin-orbit torques. The demonstrated electric-field and current control of three-terminal SCNO provides an efficient approach to developing electrically tunable microwave generators in radio frequency integrated circuits and spin-wave-based logic gates in magnonic devices.

Spin-torque nano-oscillators are promising candidates for many radio frequency and magnon-based nanodevices due to their broad frequency tunability, easy fabrication and high durability. Our new work entitled ”Controllable excitation of multiple spin wave bullet modes in a spin Hall nano-oscillator based on [Ni/Co]/Pt multilayers” is published in Nanoscale [Nanoscale, 13, 7838-7843(2021)]. To explore the tunability, in this work, we chose a [Ni/Co]/Pt-based spin Hall nano-oscillator with a moderate uniaxial anisotropy to systematically study the corresponding magnetodynamics excited by locally injecting a dc current into a nanoscale region of the extended multilayers [Ni/Co]/Pt under certain conditions. We find that the excitation current, the magnitude and orientation of magnetic field, and temperature can be used as a tool to selectively excite certain frequency bullet modes. The transition between nonlinear self-localized bullet modes with different frequencies is caused by the experimental parameter-induced change of energy landscape because, in the [Ni/Co]/Pt system, the strong spatial fluctuation of interfacial magnetic anisotropy leads to the variations of the internal magnetic field of the actual device. Our results demonstrate that the fluctuations of magnetic properties can promote experimental control of spin-torque driven magnetization dynamics in spin Hall nano-oscillators, and the application of expediting nonlinear magnetization oscillators in magnon-based devices and neuromorphic computing.

Pure spin currents, generated by nonlocal spin injection and spin-orbit effects, have been widely used to control magnetization reversal and dynamics by current without charge transfer and its side effects in the device’s actual working region. Our new work entitled”Collimated Bidirectional Propagating Spin Wave Generated by a Nonlocal Spin-Current Nano-oscillator” is published in Phys. Rev. Applied [Phys. Rev. Applied 16, 034044(2021)]. Congratulations to Dr. Lina Chen and Mr. Zhenyu Gao. In this work, we experimentally demonstrate that a single coherent spin-wave mode can be excited by the pure spin current in a nonlocal spin-injection spin-valve device. The microwave spectra show that the observed spin-wave frequency is higher than the ferromagnetic resonance frequency, and almost does not change with the excitation current at moderate magnetic fields, indicating that the observed dynamical mode is a linear propagating spin-wave mode. Furthermore, micromagnetic simulations based on our device geometry generally reproduce the experimentally observed field-dependent and current-dependent oscillation characteristics, and provide us with the additional spatial information that the spin-wave mode exhibits collimated and bidirectional propagation paths in the direction perpendicular to the applied magnetic field. Our simulation results also show that the current local Oersted field in our nonlocal device is much smaller than in conventional nanocontact magnetic oscillators, and has a minimal impact on the spin-wave dynamics. A near-symmetrically-collimated and bidirectional propagating spin-wave beam with magnetic field–controllable beam direction and current-dependent frequency, achieved in our demonstrated nonlocal spin-current nano-oscillator, can be used as a local spin-wave source for magnonic logic devices and can be used to build daisy-chaining oscillatory neural networks with mutual synchronization.