Discrete domain wall positioning due to pinning in current driven motion along nanowires.

Racetrack memory is a novel storage-class memory device in which a series of domain walls (DWs), representing zeros and ones, are shifted to and fro by current pulses along magnetic nanowires. Here we show, by precise measurements of the DW's position using spin-valve nanowires, that these positions take up discrete values. This results from DW relaxation after the end of the current pulse into local energy minima, likely derived from imperfections in the nanowire.