Giant thermal spin torque assisted magnetic tunnel junction switching

Spin-polarized charge currents induce magnetic tunnel junction(MTJ) switching by virtue of spin-transfer torque (STT). Recently,by taking advantage of the spin-dependent thermoelectric propertiesof magnetic materials, novel means of generating spin currents fromtemperature gradients, and their associated thermal-spin torques(TSTs), have been proposed, but so far these TSTs have not beenlarge enough to influence MTJ switching. Here we demonstratesignificant TSTs in MTJs by generat ing large temperature gradientsacross ultrathin MgO tunnel barriers that considerably affect theswitching fields of the MTJ. We attribute the origin of the TST to anasymmetry of the tunneling conductance across the zero-bias voltageof the MTJ. Remarkably, we estim ate through magneto-Seebeckvoltage measurements that the charge currents that would begenerated due to the temperature gradient would give rise to STTthat is a thousand times too small to account for the changes inswitching fields that we observe.