Observation of Rashba magnetism in ultra-thin ferromagnet/heavy metal heterostructures

We characterize the interplay between magnetism and spin-galvanic effects by utilizing heterostructures based on ultrathin transition metal ferromagnets (TM-FMs). An unconventional contribution to the anomalous Hall effect (AHE) and spin-orbit torques (SOTs) emerges in bilayers with heavy metals (HMs) slightly above the Curie temperature T_C. This effect vanishes when HM Pt is replaced with Pd, demonstrating the significance of SOC. We also observe anomalies in Brillouin spectra of magnetic fluctuations and magneto-optical Kerr effect measurements suggesting an unconventional contribution to magnetism. We explain our findings by the competition between exchange splitting and Rashba SOC mechanism, resulting in the emergence of a chiral magnetic state that can be described as Rashba magnetism. Our results show that optimizing the interplay between magnetism and interfacial SOC can enhance SOTs in magnetic heterostructures.