Direct measurement of current-induced fieldlike torque in magnetic tunnel junctions

We present a direct and quantitative method to measure the current-induced fieldlike torques in current perpendicular to plane magnetic multilayers. We illustrate this method on nanopillars patterned from MgO-based magnetic tunnel junctions. By measuring how the Stoner astroids are displaced, shrinked, and distorted under the influence of a bias current, we separate the contributions of the current-induced fieldlike torque, the current-induced heating, and the current-induced spin torque. In contrast to high frequency based measurement methods that are better suited to analyze the spin torque than the fieldlike term, our measurement is direct and quantitative for the current-induced fieldlike term and the heating induced reduction in shape anisotropy, while only qualitative for the spin torque.