Insight on the Time-Resolved Spin Wave Amplification in Nano-Magnonic Devices using Spin-Orbit-Torque

Abstract

Spin wave (SW) based computing i.e. magnonics relies on propagating SW as information carriers. Being quasiparticles, magnons (the SW quanta) have a fine lifetime characterizing the exponential decay of the magnons population. Consequently, up to now, all magnonic devices operate within a short time-window. Finding a SW amplification paradigm is hence a prerequisite for the development of magnonics as a credible CMOS alternative. Two schemes are envisioned for SW amplification: Parametric pumping1 and spin-orbit-torque (SOT)2. Here we will discuss SOT amplification in BiYIG/Pt bilayer3. By passing current in the Pt layer, the spin accumulation resulting from the spin-Hall effect induces a positive torque that compensate the Gilbert damping of BiYIG. At subcritical values, the current has a linear effect that decreases the losses of the system and leads to a lower effective damping. Once the current in the Pt layer reaches a threshold values, the vanishing effective damping allows for the onset of the auto-oscillation regime4. Coherent propagating spin waves are strongly scattered by auto-oscillations5 leading to a strong decrease of their attenuation length6. Here we propose an amplification mechanism that circumvent this detrimental effect. We show using micro Brillouin light scattering spectroscopy (µ-BLS) on a 500 nm Pt/BiYIG waveguide that the precise timing of the dc current in the Pt layer with respect to the radiofrequency pulse in the strip antenna enables experimental observation of a lossless propagation of spin-waves. We take advantage of the strong BLS signal of BiYIG (nearly two orders of magnitude the one of YIG3) to extensively characterize the auto-oscillations non-linear dynamic regime in the presence of SOT. Work supported by ANR grant CE24-0021(MAESTRO).