Fluctuation-Mediated Spin-Orbit Torque Enhancement in the Noncollinear Antiferromagnet Mn₃Ni_0.35Cu_0.65N

We report strong spin-orbit torques (SOTs) generated by noncollinear antiferromagnets Mn₃Ni_0.35Cu_0.65N, over a wide temperature range. The SOT efficiency peaks up to 0.3 at the Néel temperature (T), substantially higher than that of commonly studied nonmagnets, such as Pt. The sign and magnitude of the SOTs measured in our experiments are corroborated by density functional theory, confirming the dominance of the orbital Hall effect over the spin Hall effect in the nonmagnetic phase above T. In contrast, the strong temperature-dependent SOTs observed around and below T can be explained by recently developed mechanisms involving chirality-induced and extrinsic scattering-driven spin and orbital currents, considering the effect of spin fluctuations at finite temperatures. Our work not only reports a large magnitude of SOT but also sheds light on a new possible origin where orbital currents can be harnessed by leveraging the chirality of noncollinear antiferromagnets, which holds promise for magnetic memory applications.