Anisotropic magnetoresistance in colossal magnetoresistive oxide La$_{\mathrm{1-x}}$Sr$_{\mathrm{x}}$MnO$_{3}$ thin films

We present our studies of the anisotropic magnetoresitance (AMR) in colossal magnetoresistive oxide La$_{\mathrm{1-x}}$Sr$_{\mathrm{x}}$MnO$_{3}$ (LSMO, x $=$ 0.3, 0.5) thin films as a function of temperature, magnetic field and film thickness. LSMO thin films with thickness below 10 nm are grown on SrTiO$_{3}$ (001) and NdGaO$_{3}$(110) substrates via off-axis magnetron sputtering. X-ray diffraction and atomic force microscopy studies reveal high crystallinity and atomically smooth surfaces of these films. As the thickness of the films decreases, the metal insulator transition temperature (T$_{\mathrm{MI}})$ shifts to below the bulk value. Films thinner than 3 nm become totally insulating. We extract the AMR from the resistance change as a function of the orientation between current and magnetic field. AMR reaches the maximum value in the vicinity of T$_{\mathrm{MI}}$. At low magnetic field ($\sim$ 100 Oe), the angular dependence of AMR deviates from a sinusoidal shape, which is attributed to the effect of magnetocrystalline anisotropy. We discuss the effects of the carrier density, film thickness, and substrate strain on the AMR.