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.
In ferrimagnets, two sublattices with opposite magnetic moments can completely cancel the angular momentum, making the wall especially 'light' and sensitive to external influences.