Controlled Current-Driven Bi-Directional Motion of Trains of Domain Walls Along a Ferromagnetic Strip

Domain wall (DW)-based magnetic memories where each bit is represented by a single magnetic domain have repeatedly been proposed to implement faster and denser memory devices. Multilayer systems where an ultrathin ferromagnetic layer is sandwiched between a heavy metal and an oxide allow particularly fast and synchronous current-driven DW dynamics. However, an essential prerequisite for their feasibility is the efficient and precise control of DW positions. The position of the DWs can be controlled by tailoring the perpendicular magnetic anisotropy (PMA) by means of ion irradiation. Nevertheless, the current-driven dynamics of trains of DWs in these systems has not been addressed yet, either theoretically or numerically. Here, we proposed a triangular PMA periodic profile defined by two extremal values, K
_u
⁺
and K
_u
^-
(K
_u
^-
<; K
_u
⁺
), and the anisotropy period, d, showing the proposal feasibility and its bi-directional features. This paper has been carried out by means of full micromagnetic simulations and a simplified 1-D model, updated to take into account the anisotropy profile. The results highlight the suitability of using an anisotropy modulated profile to efficiently and precisely define the DW equilibrium positions.