Direct demonstration of time-reversal-symmetry-breaking spin injection from a compensated magnet

The injection, propagation and detection of spin currents are essential physical processes in spintronics. So far, the separation of charge and spin currents was facilitated by the electrical spin injection from a ferromagnet (FM) or the injection by a relativistic spin Hall effect. The devices employed are lateral spin valves comprising spatially separated injection and detection electrodes, connected by a spin-propagation channel. The time-reversal symmetry (TRS) breaking FM spin injection is realized in a geometry with an electrical bias applied between the injection electrode and the channel and is modelled by a conserved spin-polarized drift current. In contrast, the spin injection by the T-symmetric relativistic spin Hall mechanism is driven by an electrical bias applied across the injection electrode alone, and is modelled by a non-conserved spin current transverse to the applied bias. In this work, we use a lateral spin valve with a Mn5Si3 injection electrode to directly demonstrate a TRS-breaking spin injection from a compensated magnet with a vanishing net magnetization. Specifically, the TRS-breaking is demonstrated by the fact that switching between time-reversed states of the compensated magnet changes the detected spin signal. Moreover, the TRS-breaking nature of the spin injection is observed in both experimental geometries with the different electrical biasing, while using the same detection electrode. We show that this unconventional spin-injection is consistent with different magnitudes and propagation angles of electrical currents in the spin-up and spin-down channel in a d-wave altermagnet. Here our symmetry analysis and first-principles calculations are based on the compensated collinear altermagnetic order which has provided a comprehensive microscopic interpretation of earlier structural, magnetic, and anomalous Hall and Nernst measurements in Mn5Si3 thin films.