Strong current-direction dependence of anisotropic magnetoresistance in single crystalline Fe/GaAs (110) films

The longitudinal and transverse resistivities of single crystalline Fe(1 1 0) film are both experimentally studied as functions of the magnetization orientation and the current orientation with respect to the crystalline axes. Unusual dependences and symmetries are revealed but cannot be described well by established conventional models. Furthermore, the anisotropic magnetoresistance ratios differ by more than one order of magnitude for currents along different crystalline directions. Analytical expressions for the resistivities are derived by using a phenomenological model based on a series expansion of the resistivity tensor with respect to the direction cosines of the magnetization up to the fourth order. The experimental data can be fitted well by these expressions, and the resistivity coefficients obtained from the fitting are consistent with the symmetries of the current-direction dependence measurements. The resistivity coefficients increase with temperature due to electron-phonon scattering. Our studies suggest that the spin-dependent transport properties could exhibit strong magneto-crystalline effect, which paves a new way for designing future spintronics devices by taking advantage of the material crystallinity.