Control of magnetization dynamics by spin-Nernst torque

Relativistic interaction between an electron's spin and orbital angular momentum has provided an efficient mechanism to control the magnetization of nanomagnets. Extensive research has been done to understand and to improve spin-orbit-interaction-driven torques generated by nonmagnets by applying electric current. In this work, we show that heat current in a nonmagnet can also couple to its spin-orbit interaction to produce torque on the adjacent ferromagnet. Hence, this work provides a platform to study spin-orbito-caloritronic effects in heavy metal/ferromagnet bilayers.

Figure 1

Schematic representation of the experiment. (a) Schematic diagram of Pt/Py bilayer with direction of spin separation due to SHE or SNE. (b), (c) Change of linewidth (or effective damping) on application of dc spin current (generated by SHE or SNE). (d) Direction of antidamping and dampinglike torques. (e) Colored scanning electron microscopy image of the fabricated device with current and voltage terminals.

Figure 2

Characterization of spin Hall torque. (a) dc voltage generated by ST-FMR for different frequencies of the applied rf current. (b) Fit of dc voltage by $V_S$ and $V_A$. Inset of (b) shows Kittel's fit. (c) ST-FMR spectrum when dc charge current is applied perpendicular to applied rf current. (d) Modulation of the linewidth on application of dc charge current.

Figure 3

Characterization of SNT. (a) dc voltage spectrum on application of heat current along the $+Y$ axis and $-Y$ axis. (b) dc voltage spectrum when positive and negative field data points are superimposed for dc thermal gradient along the Y axis in Pt/Py sample. (c), (d) Difference in linewidth between positive and negative field values (${\mathrm{\Delta }}^{\prime }$) for different applied heater powers and different angles (θ), respectively. (e) dc voltage spectrum when positive and negative field data points are superimposed for dc thermal gradient along the Y axis in Cu/Py sample.

Figure 4

Temperature profile. (a) Surface plot of 2D thermal gradient. Estimated temperature (b) and temperature gradient (c) in Pt/Py interface.

Figure 5

Temperature calibration. (a) Temperature profile at the interface of Pt/Py. (b) Isothermal temperature contour. (c) Schematics of device structure. Arrow indicates direction of heat flow. (d) Temperature along the Y axis. (e) Temperature gradient along the Y axis.

Figure 6

(a) Simulation results of the dc voltage spectrum measured in ST-FMR at different frequencies. (b) Plot is obtained by zooming the red curve in panel a. (c) Hysteresis in the $x$ component of magnetization. (d) Real part of the susceptibilities to the magnetic field and spin current at 5-GHz frequency.