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| It is well established that spin-polarized charge currents can induce magnetic tunnel junction (MTJ) switching by virtue of spin transfer torque (STT). Recently, by taking advantage of the spin-dependent thermoelectric properties of magnetic materials, novel means of generating spin currents from temperature gradients, and their associated thermal spin torques (TSTs) have been proposed, but so far these TSTs have not been large enough to influence MTJ switching. In this talk, I will show evidence of significant TSTs in MTJs by generating large temperature gradients across ultrathin MgO tunnel barriers that considerably affect the switching fields of the MTJ. Furthermore, I will show that the TST strongly depends on the relative orientation of the free and the reference layers of the MTJ, consistent with recent theoretical work, and then discuss how the origin of the TST can be attributed to an asymmetry of the tunnelling conductance across the zero bias voltage of the MTJ. Remarkably, the estimates of the charge currents that are inevitably generated through Magneto-Seebeck voltages give rise to STT that are a thousand times too small to account for the changes in switching fields observed experimentally. |
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