Thickness-dependent angular dependent magnetoresistance in single-crystalline Co film and Co/Pt heterostructures

Abstract We report an unusual angular dependent magnetoresistance (ADMR) in single-crystalline Co films grown on Al2O3(0 0 0 1). The Co film with a thickness of 4.4 nm shows nearly zero anisotropic magnetoresistance for arbitrary magnetization orientations, and the sign of the ADMR reverses with changing Co thickness. By systematically measuring the Co-thickness-dependent anisotropic conductance in single-crystal Co/Pt, Pt/Co, and Pt/Co/Pt, we reveal that the ADMR of the Co layer grown on the Pt underlayer is significantly different from that of the Co layer grown on Al2O3(0 0 0 1). Our results suggest that the transport properties of the Co layer as a function of Pt thickness must be considered in order to better understand the spin Hall magnetoresistance in the Co/Pt bilayer.