In most magnetic materials, a domain wall, the boundary between regions with different magnetization, moves in one direction under current, set by the current's direction. But in ferrimagnets near a special point where the angular momenta of two sublattices cancel each other, the behavior changes.
Inertia of the wall's internal coordinate makes it behave like a heavy ball in a double-well potential. Depending on the current strength, the system rolls into one of the wells, corresponding to forward or backward motion. Thus, the same current can push the wall in opposite directions.
Such unusual behavior opens the way to devices where the direction of motion can be controlled simply by changing the current strength, without switching its polarity. This reduces power consumption and simplifies circuits.
as written by the authors arXiv:2603.18722
Understanding and manipulating nanoscale domain wall (DW) dynamics is a central topic in magnetism and spintronics for its promising applications in logic and memory devices. In most magnetic systems, inertia affects only transient DW dynamics, while the long-time DW motion is uniquely determined by the magnitude and direction of the applied current. Here we show that this paradigm breaks down in ferrimagnets near the angular momentum compensation point. We demonstrate that a DW can propagate steadily either forward or backward even under a direct current, with the direction controlled solely by the current strength. This anomalous phenomenon originates from the inertial dynamics of an internal DW collective coordinate, which behaves as a massive object evolving in a current-dependent double-well potential. Depending on the driving current, the system relaxes into distinct stable states associated with opposite directions of motion. Our findings reveal an unexpected role of inertia in nonlinear spin dynamics, and enable low-energy spintronic functionalities including sensitive magnetic-field detection and reconfigurable one-port devices.
In ferrimagnets, two sublattices with opposite magnetic moments can completely cancel the angular momentum, making the wall especially 'light' and sensitive to external influences.