Velocity of Domain-Wall Motion Induced by Electrical Current in the Ferromagnetic Semiconductor (Ga,Mn)As

Current-induced domain-wall motion with velocity spanning over 5 orders of magnitude up to $22\mathrm{m}/\mathrm{s}$ has been observed by the magneto-optical Kerr effect in (Ga,Mn)As with perpendicular magnetic anisotropy. The data are employed to verify theories of spin transfer by the Slonczewski-like mechanism as well as by the torque resulting from spin-flip transitions in the domain-wall region. Evidence for domain-wall creep at low currents is found.

Figure 1

(a) Layout of the device showing the $5\mu \mathrm{m}$ mesa and step for DW pinning in perpendicular magnetic anisotropy (Ga,Mn)As film. (b) $7\mu \mathrm{m}$ wide magneto-optical images with a $5\mu \mathrm{m}$ mesa in the center show that DW moves in the opposite direction to current independent of the initial magnetization orientation, and that DW displacement is proportional to pulse duration (c). The lowest panel in (b) shows destruction of ferromagnetic phase by Joule heating.

Figure 2

(a) DW velocity as a function of current at various device temperatures. The thin line and broken thin line show fitted linear and square root dependencies of velocity on current, respectively. Efficiency factor $A$ (b) and critical current density $j_C$ (c) resulting from these two fits (open and solid symbols, respectively). Broken lines are theoretically calculated assuming that spin-current polarization is equal to thermodynamic spin polarization.

Figure 3

A test of scaling law for DW creep in (Ga,Mn)As at various temperatures. Inset shows the dependence of DW velocity on current density.