Recent Progress in Proximity Coupling of Magnetism to Topological Insulators

Abstract

Inducing long‐range magnetic order in 3D topological insulators can gap the Dirac‐like metallic surface states, leading to exotic new phases such as the quantum anomalous Hall effect or the axion insulator state. These magnetic topological phases can host robust, dissipationless charge and spin currents or unique magnetoelectric behavior, which can be exploited in low‐energy electronics and spintronics applications. Although several different strategies have been successfully implemented to realize these states, to date these phenomena have been confined to temperatures below a few Kelvin. This review focuses on one strategy: inducing magnetic order in topological insulators by proximity of magnetic materials, which has the capability for room temperature operation, unlocking the potential of magnetic topological phases for applications. The unique advantages of this strategy, the important physical mechanisms facilitating magnetic proximity effect, and the recent progress to achieve, understand, and harness proximity‐coupled magnetic order in topological insulators are discussed. Some emerging new phenomena and applications enabled by proximity coupling of magnetism and topological materials, such as skyrmions and the topological Hall effect, are also highlighted, and the authors conclude with an outlook on remaining challenges and opportunities in the field.

Multifunctional two-dimensional van der Waals Janus magnet Cr-based dichalcogenide halides

“…We first examine the effect of CrSX MLs on magnetizing topological surface states (TSSs) of 3D topological insulators for the realization of QAHE 8 . We construct an vdW heterostructure with two CrSBr MLs and a six quintuple-layer Bi2Se3 (BS) thin film (CrSBr/BS/CrSBr).…”

“…The discovery of ferromagnetism at a finite temperature in atomically thin van der Waals (vdW) monolayers (MLs) [1][2][3] has spurred a surge of experimental and theoretical interests in understanding the two-dimensional (2D) magnetism and furthermore in producing emergent functionalities in 2D vdW heterostructures [4][5][6][7][8][9] . Fundamentally, the well-known Mermin-Wagner theorem based on the isotropic Heisenberg exchange model 10 suggested the absence of either FM or antiferromagnetic (AFM) order in 2D systems at nonzero temperature, and hence the early findings of FM order in CrI3 ML 1 and Cr2Ge2Te6 bilayer 11 were rather surprising.…”

“…The main advantage of these 2D magnetic vdW materials is their integrability with other vdW functional materials. Through the magnetic proximity effect, many spintronic, valleytronic and optoelectronic properties can be achieved in heterostructures by stacking diverse 2D vdW MLs or ultrathin films 5,7,8 . For example, the quantum anomalous Hall effect (QAHE) and axion insulator phase can be realized by integrating 2D FM semiconductors with thin films of topological insulators 8,[12][13][14][15] .…”

Robust Subthermionic Topological Transistor Action via Antiferromagnetic Exchange

“…The above scenario can be realized by the addition of AF exchange interaction, which can be incorporated via proximity coupling [42] to a 2D topological insulator implying the addition of the term M AF τ z σ z to the low-energy Hamiltonian in (1). As represented by the points (1),( 2) and (3) in Fig.…”

“…However, this also introduces dissipative conduction modes from the bulk in the ON state, defeating one of the desired attributes in a TQFET. As a tactical solution, we demonstrate that the introduction of out-of-plane antiferromagnetic exchange interaction, which can be induced via proximity coupling [42] restores the dissipationless ON state and can effectively reap the merits expected from the Rashba-assisted TQFET.…”