Magnetoresistance Anomalies Across Domain Walls in Tensile Strained (Ga,Mn)As

We describe measurements of the anomalous Hall effect (AHE), planar Hall effect and anisotropic magnetoresistance (AMR) in tensile-strained (Ga,Mn)As epilayers with relatively high Curie temperatures ($125 \rm{K} < T_{\rm{C}} < 135 \rm{K}$). Samples are grown on a strain-relaxed (Ga,In)As buffer layer deposited on (001) GaAs, creating an in-plane tensile strain that orients the easy axis of the magnetization along [001]. We measure magnetoresistance as a function of the magnetic field vector $\vec{H}$ and temperature ($4.2 \rm{K} < T < 150 \rm{K}$) using Hall bars oriented along $[110]$,$[1 \overline{1} 0]$ and $[100]$. AMR measurements reveal striking antisymmetric resistance anomalies as we sweep either the magnitude or angle of $\vec{H}$. These anomalies originate in a strong AHE contribution to the AMR when measurements are made across domain walls in the presence of slight sample misorientation, providing a sensitive probe of the nucleation and propagation of magnetic domain walls up to temperatures as high 120K. Work supported by DARPA, ONR and NSF.