Domain wall attraction and repulsion during spin-torque-induced coherent   motion
  We calculate the interaction between two magnetic domain walls during their current-induced motion. This interaction produces a separation-dependent resistance and also a differential velocity, causing domains in motion to experience an effective attraction at large separations and an effective repulsion at short separations. In an intermediate range of currents the two domain walls will reach a natural equilibrium spacing that depends on the magnitude of the current flowing through the material. 
E. A. Golovatski and M. E. Flatt\'e
cond-mat.mes-hall