Magnetization switching at the interface between ferromagnetic and paramagnetic metals, controlled by current-induced torques, could be exploited in magnetic memory technologies. Compelling questions arise regarding the role played in the switching by the spin Hall effect in the paramagnet and by the spin-orbit torque originating from the broken inversion symmetry at the interface. Of particular importance are the antidamping components of these current-induced torques acting against the equilibrium-restoring Gilbert damping of the magnetization dynamics. Here, we report the observation of an antidamping spin-orbit torque that stems from the Berry curvature, in analogy to the origin of the intrinsic spin Hall effect. We chose the ferromagnetic semiconductor (Ga,Mn)As as a material system because its crystal inversion asymmetry allows us to measure bare ferromagnetic films, rather than ferromagnetic-paramagnetic heterostructures, eliminating by design any spin Hall effect contribution. We provide an intuitive picture of the Berry curvature origin of this antidamping spin-orbit torque as well as its microscopic modelling. We expect the Berry curvature spin-orbit torque to be of comparable strength to the spin-Hall-effect-driven antidamping torque in ferromagnets interfaced with paramagnets with strong intrinsic spin Hall effect. In one interpretation discussed in the literature so far, currentinduced switching at ferromagnet/paramagnet interfaces 1,2 originates from an antidamping component of the spin-orbit torque (SOT) 1, at the broken space-inversion-symmetry interface, while in another 2,23,25 , the spin Hall effect (SHE) [26][27][28][29][30][31][32] in the paramagnet combines with the antidamping spin-transfer torque (STT) [33][34][35][36] in the ferromagnet. Because, so far, the theories have considered a scattering-related SOT with an antidamping component that is expected to be relatively weak compared with the field-like SOT component 18,19 , much attention has been focused on the SHE-STT interpretation, in which the large SHE originates from the Berry curvature in the band structure of a clean crystal 2,28,29,37 . The focus of the present work is on a large antidamping SOT that stems from a Berry curvature origin analogous to intrinsic SHE.In conventional semiclassical transport theory, the linear response of the carrier system to the applied electric field is described by the non-equilibrium distribution function of carrier eigenstates, which are considered to be unperturbed by the electric field. The form of the non-equilibrium distribution function is obtained by accounting for the combined effects of the carrier acceleration in the field and of scattering. For the SOT, the non-equilibrium distribution function can be used to evaluate the currentinduced carrier spin density, which then exerts the torque on the magnetization via carrier-magnetic moment exchange coupling. The field-like component of the SOT reported in previous theoretical and experimental studies in (Ga,Mn)As films 4,8,9,11,24 and pred...

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Recently discovered relativistic spin torques induced by a lateral current at a ferromagnet/ paramagnet interface are a candidate spintronic technology for a new generation of electrically controlled magnetic memory devices. The focus of our work is to experimentally disentangle the perceived two model physical mechanisms of the relativistic spin torques, one driven by the spin-Hall effect and the other one by the inverse spin-galvanic effect. Here, we show a vector analysis of the torques in a prepared epitaxial transition-metal ferromagnet/ semiconductor-paramagnet single-crystal structure by means of the all-electrical ferromagnetic resonance technique. By choice of our structure in which the semiconductor paramagnet has a Dresselhaus crystal inversion asymmetry, the system is favourable for separating the torques due to the inverse spin-galvanic effect and spin-Hall effect mechanisms into the field-like and antidamping-like components, respectively. Since they contribute to distinct symmetry torque components, the two microscopic mechanisms do not compete but complement each other in our system.