Principal Investigator Jongyoon Han
Antiferromagnetic materials show promises compared to ferromagnetic materials for spintronic devices due to their immunity to external magnetic fields and their ultra-fast dynamics. However, difficulties in controlling and determining their magnetic state are limiting their technological applications. At the compensation point, the two antiparallel sub-lattices in a ferrimag- net have the same magnetic moment, and the material is an antiferromagnet. Compensated ferrimagnets are expected to exhibit fast magnetic dynamics like an antiferromagnet, and yet their magnetic state can be manipulated and detected like a ferromagnet, and therefore, have been pursued as a candidate system for ultrafast spintronic applications. Previously, it was demonstrated that current-induced spin-orbit torque could provide an efficient switching mechanism for a compensated ferrimagnet. However, limited by the quasi-static measurement technique, the nature of the switching dynamics in these experiments is yet to be revealed. In this work, we provide the first experimental proof of current-induced fast domain wall (DW) mo- tion in a compensated ferrimagnet.
Using a magneto-optic Kerr effect microscope, we determine the spin-orbit torque-induced DW motion in Pt/Co1-xTbx microwires with perpendicular mag- netic anisotropy. The DW velocity is determined as a function of applied current amplitude. A large en- hancement of the DW velocity is observed in angular momentum compensated Pt/Co0.74Tb0.26 microwires compared to single layer or multi-layer ferromagnetic wires. Using analytical model, we also find that near angular momentum compensation point, the domain walls do not show any velocity saturation unlike ferromagnets or uncompensated ferrimagnets since both the effective gyromagnetic ratio and effective damping diverge at this composition. Moreover, by studying the dependence of the domain wall velocity with the longitudinal in-plane field, we identify the structures of ferrimagnetic domain walls across the compensation points. The high current-induced domain wall mobility and the robust domain wall chirality in compensated ferrimagnets open new opportunities for spintronic logic and memory devices.