Temperature dependence of spin-orbit torques in a bulk perpendicularly magnetized Tb$_{\mathrm{x}}$Co$_{\mathrm{1-x}}$ alloy film

Current-driven spin-orbit torques (SOTs) in ultra-thin ferromagnet/heavy metals with strong spin orbit coupling has been shown to be efficient way for manipulating magnetization [1,2]. Damping-like (DL) SOT is most relevant to highly efficient magnetization switching due to spin Hall effect [2]. Recently, some groups have reported SOT efficiency in ferrimagnet alloy films with bulk perpendicular magnetic anisotropy, which becomes potential candidate for the futures spin-orbit device with large thermal stability [3-5]. However, mechanism of spin transport still remains questionable issues in magnetic compensated ferrimagnet alloy film strongly depending on the temperature and composition. Here, we report DL-SOT efficiency ($\chi_{\mathrm{DL}})$ for various temperatures in a Ta/Tb$_{\mathrm{x}}$Co$_{\mathrm{1-x}}$ bi-layers film, characterized by conventional harmonic voltage measurement. As decreasing temperature, coercively field ($H_{\mathrm{c}})$ showed an increase and decrease below 200 K, whereas the saturation magnetization ($M_{\mathrm{s}})$ does opposite behavior to the $H_{\mathrm{c}}$, since two sub-lattices of Co and Tb are equal in magnitude due to the magnetic compensation point ($T_{\mathrm{M}})$. Furthermore, it is found that $\chi _{\mathrm{DL}}$ showed the maximum, approaching to $T_{\mathrm{M}}$. This result is consistent with a relation that $\chi_{\mathrm{DL}}$ is inversely proportional to $M_{\mathrm{s}}$ [5].