Geometrical considerations to discern the transverse spin Nernst effect in an all-metallic permalloy/platinum bilayer system

Abstract

Most spin caloritronics research utilizes thin films on substrates with an in-plane heat flow, where an unintended out-of-plane thermal gradient may develop by heat dissipation through the substrate. In systems exploiting metallic ferromagnets to generate or detect spin currents, such out-of-plane thermal gradients might confuse the signal via undesirable thermomagnetic effects, such as the anomalous Nernst effect. Here, we report direct measurement of the spin current created by the spin Nernst effect in platinum, using ferromagnetic metal contacts as spin accumulation detectors. By comparing the voltage measured transverse and longitudinal to the thermal gradient, we find that the device geometry is crucial in all-metallic systems. Exploiting the orthogonality in the angular dependence on the external magnetic field of the transversely measured voltage, we quantitatively separate the spin Nernst signal from the parasitic anomalous Nernst voltage, which are of the same order of magnitude. As a result, we estimate the spin Nernst angle of platinum to be comparable to the spin Hall angle in magnitude with an opposite sign.