Weak temperature dependence of orbital Hall angle in Ta/Ni bilayers

Abstract In spintronics, characterizing the temperature dependence of spin Hall angle (SHA) has been a common method to explore the underlying mechanisms of spin Hall effect (SHE). However, the experimental reports of orbital Hall effect (OHE) under varying temperatures remain limited. Here, we systematically investigate the effective charge-to-spin conversion efficiency θ _H in Ta/Ni and Ta/CoFeB bilayers across the temperature ranging from 10 K to 300 K, where the θ _H represents the combined contribution of the SHA and the orbital Hall angle (OHA). The θ _H of Ta/Ni remains positive across the investigated temperature range, indicating that the OHE dominates over the SHE. The Ta/CoFeB sample serves as a reference with negligible OHE, exhibiting negative values of θ _H that are consistent with the SHA of Ta. As temperature decreases, the θ _H of both Ta/Ni and Ta/CoFeB increase with similar trends. Due to the significantly smaller difference of SHAs in Ta/Ni and Ta/CoFeB compared to those of OHAs, we suggest that the similar trends of θ _H demonstrate the weak temperature dependence of OHA in Ta/Ni. This finding advances the comprehensive understanding of OHE and may pave the way for the application of orbitronics.