Non-local magnon-based transport in yttrium iron garnet/platinum heterostructures at high temperatures

Abstract

The spin Hall effect in a heavy metal thin film allows to probe the magnetic properties of an adjacent magnetic insulator via magnetotransport measurements. Here, we investigate the magnetoresistive response of yttrium iron garnet/platinum heterostructures from room temperature to beyond the Curie temperature $T_{\mathrm{C},\mathrm{YIG}}\approx 560\mathrm{K}$ of the ferrimagnetic insulator. We find that the amplitude of the (local) spin Hall magnetoresistance decreases monotonically from $300\mathrm{K}$ towards $T_{\mathrm{C}}$, mimicking the evolution of the saturation magnetization of yttrium iron garnet. Interestingly, the spin Hall magnetoresistance vanishes around $500\mathrm{K}$, well below $T_{\mathrm{C}}$, which we attribute to the formation of a parasitic interface layer by interdiffusion. Around room temperature the non-local magnon-mediated magnetoresistance exhibits a power law scaling $T^{\alpha }$ with $\alpha =3/2$, as already reported. The exponent decreases gradually to $\alpha \sim 1/2$ at around $420\mathrm{K}$, before the non-local magnetoresistance vanishes rapidly at a similar temperature as the spin Hall magnetoresistance. We attribute the reduced $\alpha$ at high temperatures to the increasing thermal magnon population which leads to enhanced scattering of the non-equilibrium magnon population and a reduced magnon diffusion length. Finally, we find a magnetic field independent offset voltage in the non-local signal for $T>470\mathrm{K}$ which we associate with electronic leakage currents through the normally insulating yttrium iron garnet film. Indeed, this non-local offset voltage is thermally activated with an energy close to the band gap.

7 pages, 4 figures