Theory of Spin-splitter Magnetoresistance in Altermagnets

Abstract

We develop a theory of angle-dependent magnetoresistance (ADMR) in metallic altermagnets coupled to ferromagnetic insulators and establish criteria that distinguish them from conventional compensated magnets with spin-orbit coupling. We show that the spin-splitter magnetoresistance (SSMR) reported by H. Chen et al. [Adv. Mater. 37, 2507764 (2025)] constitutes a smoking-gun signature of collinear altermagnetism in metallic systems. In contrast to spin-Hall magnetoresistance (SMR), SSMR exhibits three key distinctions: it depends solely on the relative orientation between the ferromagnetic magnetization and the altermagnetic N\'eel vector, yields a longitudinal ADMR response of opposite sign, and features a direct proportionality between longitudinal and transverse ADMR signals, absent in SMR. These results provide a clear route to unambiguously identify altermagnets in transport.