Current-induced domain wall motion in ferromagnetic semiconductors

Low magnetization ($\sim $0.05 T) and high spin-polarization in ferromagnetism of transition metal-doped GaAs allow us to explore a number of spin-dependent phenomena not readily accessible in metal ferromagnets. Spin-polarized current induced domain wall (DW) motion in (Ga,Mn)As [1, 2] reveals rich physics resulting from the interaction between spin-polarized electrons and localized spins inside a magnetic DW. By using a 30 nm thick (Ga,Mn)As layer ($x_{Mn}$ = 0.045) with perpendicular magnetic anisotropy, we have measured by magneto-optical Kerr microscopy a wide range of velocity-current density curves in the sample temperature range of 97 -- 107 K. Two regimes are found in the current density dependence of the DW velocity. At high-current densities ($>$ 2 x 10$^{5}$ A/cm$^{2})$, the domain wall velocity is approximately a linear function of the current density above a threshold current density. This result will be compared to the recent theories of DW motion. At low-current densities, the functional form of the velocity-current curves follow an empirical scaling law, obtained by modifying the one for magnetic-field induced creep. This shows that current-induced DW creep is present. We have also determined the intrinsic resistance of the DW in a similar configuration [3]. \begin{enumerate} \item M. Yamanouchi, D. Chiba, F. Matsukura, and H. Ohno, Nature \textbf{428}, 539 (2004). \item M. Yamanouchi, D. Chiba, F. Matsukura, T. Dietl and H. Ohno, Phys. Rev. Lett. \textbf{96}, 096601 (2006). \item D. Chiba, M. Yamanouchi, F. Matsukura, T. Dietl, and H. Ohno, Phys. Rev. Lett. \textbf{96}, 096602 (2006). \end{enumerate}