Abstract
Nonlocal spin injection has been recognized as an efficient mechanism for creation of pure spin currents not tied to the electrical charge transfer. Here we demonstrate experimentally that it can induce coherent magnetization dynamics, which can be utilized for the implementation of novel microwave nano-sources for spintronic and magnonic applications. We show that such sources exhibit a small oscillation linewidth and are tunable over a wide frequency range by the static magnetic field. Spatially resolved measurements of the dynamical magnetization indicate a relatively large oscillation area, resulting in a high stability of the oscillation with respect to thermal fluctuations. We propose a simple quasilinear dynamical model that reproduces well the oscillation characteristics.
Highlights
Nonlocal spin injection has been recognized as an efficient mechanism for creation of pure spin currents not tied to the electrical charge transfer
The resulting spin-transfer torque (STT) enhances fluctuations of the Py magnetization, which can be described as effective negative dynamic damping
Previous studies of in-plane magnetized nano-oscillators driven by the spin-polarized currents or by spin Hall effect (SHE) have been successfully interpreted in terms of the nonlinear dynamical self-localization mechanism[28,32]
Summary
Nonlocal spin injection has been recognized as an efficient mechanism for creation of pure spin currents not tied to the electrical charge transfer. We report an experimental observation of magnetization auto-oscillations due to the injection of pure spin current in a nonlocal spin valve structure We demonstrate that this mechanism enables generation of coherent magnetization precession with the frequency tunable in the range 6–12 GHz and the linewidth below 20 MHz. Spatially resolved measurements show that, to the conventional spin-torque and spin-Hall nanooscillators with in-plane magnetization, the auto-oscillation mode excited by the pure spin current in the nonlocal spin valve devices is a localized mode with the frequency below the spectrum of propagating spin waves. In contrast to most of the previously studied devices, the localization area is relatively large (about 300 nm), suggesting that the spatial extent of the auto-oscillation mode is not significantly affected by the nonlinear selflocalization effects, but is rather determined by the spin-diffusion length in the current-carrying electrode This conclusion is reinforced by the results of micromagnetic simulations based on a simple linear normal-mode model that provide a good agreement with the experimental data
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