Evidence of Long-Range Dzyaloshinskii–Moriya Interaction at Ferrimagnetic Insulator/Nonmagnetic Metal Interfaces

Abstract

The Dzyaloshinskii-Moriya interaction (DMI) is a chiral magnetic exchange interaction promoting the perpendicular alignment of neighboring spins. The DMI typically occurs in materials characterized by inversion asymmetry and strong spin-orbit coupling, such as ferromagnetic/nonmagnetic metal (FM/NM) interfaces. The microscopic origin of this interfacial DMI is commonly described by the three-site Levy–Fert model, where neighboring atomic moments interact through the vicinal non-magnetic atoms. Herein, evidence of substantial DMI arising from long-range interactions with a non-local interface is shown, extending the conventional viewpoint. The interfacial DMI in a ferrimagnetic insulator, Tb₃Fe₅O₁₂ (TbIG), is measured as a function of thickness and interfaced with various NMs. By correlating the DMI with the interfacial spin transport and atomically-resolved electron microscopy, the TbIG/NM interface is identified as the dominant source of DMI in these structures. Using Cu as a spacer modifies the interfacial DMI substantially due to a long-range interaction of TbIG with the Cu/NM interface. Density functional theory calculations on similar structures support these experimental findings and the proposed interpretation. These results provide new insights into the fundamental understanding and engineering of interfacial DMI and will stimulate research in other materials with overarching implications for domain wall and skyrmion-based devices.