Intrinsic and Extrinsic Unity for Chiral-Spin Alignment and Charge-to-Spin Conversion Induced by the Rashba-Edelstein Effect.

Reducing the dimensionality in layered materials typically yields properties distinct from bulk properties. In systems with broken inversion symmetry, strong spin-orbit coupling induces relativistic electron interactions such as the Rashba-Edelstein effect (REE). Initially proposed in two-dimensional magnets, applying the REE theory to real three-dimensional systems poses challenges, necessitating experimental validation. In this study, we empirically ascertained an REE-induced intrinsic and extrinsic fundamental unity between two distinct and dissimilar phenomena, namely, charge-to-spin conversion and chiral-spin alignment. Atomically thin quasi-two-dimensional ferromagnetic materials were used to observe such universal unity by examining the thickness dependences of the Heisenberg exchange interaction, the Dzyaloshinskii-Moriya interaction, and spin-orbit torques. The results revealed a correlation that is highly consistent with the underlying theoretical REE model. These findings not only highlight the role of REE in fundamental physics but also illuminate the intricate impact of interfacial effects on magnetic materials.