Spectroscopic confirmation of linear relation between Heisenberg- and interfacial Dzyaloshinskii-Moriya-exchange in polycrystalline metal films

Abstract: Proposals for novel spin-orbitronic logic1 and memory devices2 are often predicated on assumptions as to how materials with large spin-orbit coupling interact with ferromagnets when in contact. Such interactions give rise to a host of novel phenomena, such as spin-orbit torques3,4 , chiral spin-structures5,6 and chiral spin-torques. These chiral properties are related to the anti-symmetric exchange, also referred to as the interfacial Dzyaloshinskii-Moriya interaction (DMI)9,10. For numerous phenomena, the relative strengths of the symmetric Heisenberg exchange and the DMI is of great importance. Here, we use optical spin-wave spectroscopy (Brillouin light scattering) to directly determine the DMI vector for a series of Ni80Fe20/Pt samples, and then compare the nearest-neighbor DMI coupling energy with the independently measured Heisenberg exchange integral. We find that the Ni80Fe20-thickness-dependencies of both the microscopic symmetric- and antisymmetric-exchange are identical, consistent with the notion that the basic mechanisms of the DMI and Heisenberg exchange essentially share the same underlying physics, as was originally proposed by Moriya11. While of significant fundamental importance, this result also leads us to a deeper understanding of DMI and how it could be optimized for spin-orbitronic applications.