Manipulating Spin‐Lattice Coupling in Layered Magnetic Topological Insulator Heterostructure via Interface Engineering

Abstract Induced magnetic order in a topological insulator (TI) can be realized either by depositing magnetic adatoms on the surface of a TI or engineering the interface with epitaxial thin film or stacked assembly of 2D van der Waals (vdW) materials. Herein, the observation of spin‐phonon coupling in the otherwise non‐magnetic TI Bi 2 Te 3 is reported, due to the proximity of FePS 3 (an antiferromagnet (AFM), T N ≈ 120 K), in a vdW heterostructure framework. Temperature‐dependent Raman spectroscopic studies reveal deviation from the usual phonon anharmonicity originated from spin‐lattice coupling at the Bi 2 Te 3 /FePS 3 interface at/below 60 K in the peak position (self‐energy) and linewidth (lifetime) of the characteristic phonon modes of Bi 2 Te 3 (106 and 138 cm −1 ) in the stacked heterostructure. The Ginzburg‐Landau (GL) formalism, where the respective phonon frequencies of Bi 2 Te 3 couple to phonons of similar frequencies of FePS 3 in the AFM phase, is adopted to understand the origin of the hybrid magneto‐elastic modes. At the same time, the reduction of characteristic T N of FePS 3 from 120 K in isolated flakes to 65 K in the heterostructure, possibly due to the interfacial strain, which leads to smaller Fe‐S‐Fe bond angles as corroborated by computational studies using density functional theory (DFT). Besides, inserting hexagonal boron nitride within Bi 2 Te 3 /FePS 3 stacking regains the anharmonicity in Bi 2 Te 3 . Controlling interfacial spin‐phonon coupling in stacked heterostructure can have potential application in surface code spin logic devices.