Interplay of spin-orbit torque and thermoelectric effects in ferromagnet/normal-metal bilayers

Abstract

We present harmonic transverse voltage measurements of current-induced thermoelectric and spin-orbit torque (SOT) effects in ferromagnet/normal metal bilayers, in which thermal gradients produced by Joule heating and SOT coexist and give rise to ac transverse signals with comparable symmetry and magnitude. Based on the symmetry and field-dependence of the transverse resistance, we develop a consistent method to separate thermoelectric and SOT measurements. By addressing first ferromagnet/light metal bilayers with negligible spin-orbit coupling, we show that in-plane current injection induces a vertical thermal gradient whose sign and magnitude are determined by the resistivity difference and stacking order of the magnetic and nonmagnetic layers.We then study ferromagnet/heavy metal bilayers with strong spin-orbit coupling, showing that second harmonic thermoelectric contributions to the transverse voltage may lead to a significant overestimation of the antidamping SOT. We find that thermoelectric effects are very strong in Ta(6nm)/Co(2.5nm) and negligible in Pt(6nm)/Co(2.5nm) bilayers. After including these effects in the analysis of the transverse voltage, we find that the antidamping SOTs in these bilayers, after normalization to the magnetization volume, are comparable to those found in thinner Co layers with perpendicular magnetization, whereas the field-like SOTs are about an order of magnitude smaller.

Spin transport in as-grown and annealed thulium iron garnet/platinum bilayers with perpendicular magnetic anisotropy

“…36 The appearance of the former is due to oscillations of the magnetization vector m around its equilibrium position mediated by the oscillating current-induced SOTs and Oersted field. The latter appears due to the quadratic dependence of the Joule heating on the injected current ( ), which unavoidably establishes a temperature gradient ( T) perpendicular to the layer plane due to preferential heat dissipation towards the substrate side.…”

Anomalous Current-Induced Spin Torques in Ferrimagnets near Compensation

“…The peak value of HL and HT corresponds to the spin efficiency (akin to the spin Hall angle) of 0.52 and 0.44, respectively. These values are at least three times higher compared to other Pt/FM systems [42,47,48].…”

Temperature dependence of spin-orbit torques across the magnetic compensation point in a ferrimagnetic TbCo alloy film

“…SOTs with both a fieldlike and dampinglike character can manifest in such systems, with the latter capable of driving magnetization switching [1][2][3][4][5]7,9,[11][12][13]15,21,22,24] and magnetic domain wall motion [26][27][28][29][30][31]. SOTs have been identified and quantified by a variety of techniques including spin-torque ferromagnetic resonance [2,7,14,17,19,25], quasistatic magnetization tilting probed through harmonic voltage measurements [6,[8][9][10][11][12][13]17,[19][20][21][22][23][24][25][26]28,31], and current-induced hysteresis loop shift measurements [18,32,33]. Most studies of SOTs have focused on ultrathin metallic ferromagnet/heavy-metal bilayers with interfacial perpendicular magnetic ani...…”