Sustained RF oscillations from thermally induced spin-transfer torque

Abstract: We investigate the angular dependence of the spin torque generated when applying a temperature difference across a spin-valve. Our study shows the presence of a non-trivial fixed point in this angular dependence, i.e. the possibility for a temperature gradient to stabilize radio frequency oscillations without the need for an external magnetic field. This so called "wavy" behavior can already be found upon applying a voltage difference across a spin-valve but we find that this effect is much more pronounced with a temperature difference. Our semi-classical theory is parametrized with experimentally measured parameters and allows one to predict the amplitude of the torque with good precision. Although thermal spin torque is by nature less effective than its voltage counterpart, we find that in certain geometries, temperature differences as low as a few degrees should be sufficient to trigger the switching of the magnetization.