Domain-wall (DW) based spintronics devices rely on moving domain walls in confined geometries such as narrow ferromagnetic wires. The higher the speed of the domain wall, the faster are these devices. Domain wall velocities typically range from 1 m/s to 100 m/s, and are determined by the driving source and geometry. Walls are pushed along by magnetic fields or by spin-polarized currents. The dependence of domain wall velocity ν on magnetic field H is usually defined by the mobility curve model description by Schryer and Walker [1]. At relatively low fields, the velocity is known to scale linearly with the field, ν˜H, up to a certain limiting field (the so-called “Walker breakdown field” or equivalently the “Walker breakdown current” and more generally the “Walker breakdown limit”) at which the wall velocity peaks. According to this model, above that field, the domain wall motion becomes turbulent, leading to a reduction of ν with increasing H, until at large fields ν increases again [2]. A similar dependence holds if a spin-polarized current is used rather than a field.
A prototypical domain wall device is the magnetic racetrack [3, 4], alternatives are logic concepts such as Cowbum's magnetic domain wall logic [5]. The domain walls, shuttled through the circuit by current or field, need to stay intact to the extent that the intended logic operation can be performed. Therefore, the applied field or current is kept low to ensure that one stays in the linear regime of the mobility curve and, correspondingly, velocities remain limited.
The possibility to manipulate the dynamic response of a DW and to enhance DW velocity beyond the Walker breakdown limit has been proposed. However, the realization of a practical device [3, 8] that implements high DW velocities remains elusive due to the technological complexity or due to the modest velocity increase.
The references provided at the end of the present description provide useful information as to the background art of the present invention.