Spin-Hall and anisotropic magnetoresistance in ferrimagnetic Co-Gd/Pt layers

We present the Co-Gd composition dependence of the spin-Hall magnetoresistance (SMR) and anisotropic magnetoresistance (AMR) for ferrimagnetic $\mathrm{C}{\mathrm{o}}_{100\ensuremath{-}x}\mathrm{G}{\mathrm{d}}_{x}/\mathrm{Pt}$ bilayers. With Gd concentration $x$, its magnetic moment increasingly competes with the Co moment in the net magnetization. We find a nearly compensated ferrimagnetic state at $x=24$. The AMR changes sign from positive to negative with increasing $x$, vanishing near the magnetization compensation. On the other hand, the SMR does not vary significantly even where the AMR vanishes. These experimental results indicate that very different scattering mechanisms are responsible for AMR and SMR. We discuss a possible origin for the alloy composition dependence.