Current-induced magnetic domain wall motion in compensated ferrimagnet*

Antiferromagnets (AFMs) show promises compared to ferromagnets for spintronic devices due to their immunity to external magnetic fields and their ultra-fast dynamics. But the challenges in controlling and determining their magnetic state are limiting their technological applications. At the compensation point, the two antiparallel sub-lattices in a ferrimagnets have the same magnetic moment and the material is an AFM. Compensated ferrimagnets are expected to exhibit fast magnetic dynamics like an AFM and yet their magnetic state can be manipulated and detected like a ferromagnet, and therefore, have been pursued as a candidate system for fast spintronic applications. In this work, we provide the first experimental proof of current-induced fast domain wall (DW) motion in a compensated ferrimagnet. Using a magneto optic Kerr effect microscope, we determine the spin orbit torque-induced DW motion in Pt/Co_1-xTb_x with perpendicular magnetic anisotropy. We find that close to the angular momentum compensation, the DW mobility increases significantly, reflecting the fast magnetic dynamics in this regime. Moreover, by studying the dependence of the domain wall velocity with the in-plane field, we identify the structures of ferrimagnetic domain walls across the compensation points.