Spin Current Control of Damping in YIG/Pt Nanowires

Insulating ferromagnet(IF)/normal metal(NM) interfaces are important for understanding of pure spin current injection and have great potential for spintronic applications. Here we report studies of the effect of pure spin currents on damping of spin wave eigenmodes in YIG(30 nm)/Pt(6 nm) bilayer nanowires that are 60–250 nm wide and 1–13 um long. The samples show magneto-resistance (MR) arising from two distinct mechanisms: (i) spin Hall magnetoresistance (SMR) and (ii) inverse spin Hall effect (iSHE) in conjunction with spin Seebeck current (SSC) induced by Ohmic heating of the Pt layer. Utilizing the SMR and iSHE effects, we measure the properties of spin wave eigenmodes of the nanowires by spin-torque ferromagnetic resonance (ST-FMR) with magnetic field modulation.
Application of direct current to the Pt layer results in injection of spin Hall current into YIG that acts as either damping or anti-damping spin torque depending on the current polarity. In addition, Ohmic heating in Pt gives rise to a SSC injected into YIG, which acts as anti-damping torque independent of the current polarity. ST-FMR measurements reveal current-induced variation of the linewidth of spin wave modes that is asymmetric in the bias current as shown in Fig. 1. The linewidth decreases to zero for the current polarity that gives rise to anti-damping spin Hall torque. Near this current value, we observe complex interaction among the spin wave eigenmodes of the nanowire that we asses using micromagnetic simulations. Our results advance understanding of magnetization dynamics driven by pure spin currents in nanoscale IF/NM systems.