Bias field dependence of domain drag propagation velocities in GdCoAu bubble films

The bias field dependence of the velocity of bubble propagation by the domain drag effect was studied in a GdCoAu amorphous film. Bubbles in close-packed arrays were propagated by pulsing currents directly through a stripline of the material fabricated by photolithography and ion-beam milling. As bias field is increased, at given current and pulse width, the velocity decreases, passes through a minimum, then increases again. The domain drag drive field at a given bias is derived both from the critical current at which motion begins and from the slope of velocity with current. A theory for the domain drag drive field Hd of a bubble raft with infinite length along the current direction is derived, giving the simple result Hd /βjD = 1/2(d0/D) -(π/4√3)(d0/D)3, where β is the Hall angle, j is the current density, d0 is the bubble diameter, and D is the nearest-neighbor spacing. Experimental results from critical current agree approximately with the theory, but results from velocity slope with current are a factor of 3 too high.