Exchange Coupling Torque in Ferrimagnetic Bi-layer Systems at the Angular Momentum Compensation Temperature

Within the last decade, the efficiency of current-induced motion of magnetic domain walls (DWs) has been enhanced tremendously by utilizing the exchange coupling torque (ECT) in synthetic antiferromagnets. In this talk we show that this mechanism also applies to ferrimagnetic layers consisting of a transition metal layer and a rare earth metal layer which couple antiferromagnetically. The motion is most efficient when the angular momenta of both layers compensate each other and the ECT is maximized. Additionally, we demonstrate that at angular momentum compensation a magnetic field, which is applied along the effective Dzyaloshinskii-Moriya interaction field, has no influence on the DW velocity. By changing the temperature of a Co/Gd ferrimagnetic bi-layer, we can to tune the ratio of angular momenta of Co and Gd and identify the angular momentum compensation temperature T_A. Since the device temperature is significantly increased by the current pulses, taking into account Joule heating is of major importance. The presented findings can be used for the development of novel storage devices and improving their efficiency.