Interface Engineering Enabled Low Temperature Growth of Magnetic Insulator on Topological Insulator

Abstract

Realization of the quantum anomalous Hall (QAH) effect has been demonstrated in several magnetic topological insulators (MTIs). MTIs can be synthesized by doping magnetic elements into topological insulators (TIs) [1][2][3][4][5][6][7][8][9] or growth of intrinsic MTI compounds. [10][11][12][13][14][15][16][17][18][19] However, these MTI materials require temperatures much lower than their magnetic T c to achieve quantization in the Hall effect. This deficiency has been attributed to inhomogeneity in magnetic doping which causes localized variation in surface state exchange gaps. Magnetism can also be induced in the surface of TI thin films via proximity exchange effect. This proximity induced magnetization (PIM) is envisioned by coupling TIs with a magnetic insulator (MI). PIM in TIs have been experimentally confirmed in heterostructures of TIs with magnetic insulators (MIs) such as rare earth garnets and EuS, [20][21][22][23][24][25][26][27][28] MTIs, [29,30] and telluride van der Waals (vdW) magnets. [31] However, recent studies have pointed out the complexities in measuring proximity exchange in these systems, [31] which can be affected by a number of problems such as diffusion at the interface and band bending. Thus, providing a barrier for diffusion while permitting magnetic exchange in TI/MI heterostructures will be necessary for devices, and it is shown here that a TiO x interface barrier achieves this goal. Only a single study by Watanabe et al. [31] has shown PIM and QAH in a TI/MI/TI thin film sandwich structure of (Zn,Cr)Te/(Bi,Sb) 2 Te 3 /(Zn,Cr)Te. However, even in this material system, the QAH effect was seen at extremely low temperature of 0.03 K. This low temperature is possibly due to: (1) High-quality MIs which were grown on TI thin films have very low Curie temperature, T c , such as (Zn,Cr) Te with T c < 40 K [31] and EuS with T c of ≈17 K. [25] (2) Even with 20-25% of the magnetic species, Cr in (Zn,Cr)Te, finite localized nonmagnetic nanoregions may exist in the samples.MIs such as rare-earth garnets and ferrites are excellent materials that are magnetically ordered well above room-temperature, making them ideal candidates for QAH materials coupled with TIs. However, growth of MIs on top of TIs using Combining topological insulators (TIs) and magnetic materials in heterostructures is crucial for advancing spin-based electronics. Magnetic insulators (MIs) can be deposited on TIs using the spin-spray process, which is a unique nonvacuum, low-temperature growth process. TIs have highly reactive surfaces that oxidize upon exposure to atmosphere, making it challenging to grow spinspray ferrites on TIs. In this work, it is demonstrated that a thin titanium capping layer on TI, followed by oxidation in atmosphere to produce a thin TiO x interfacial layer, protects the TI surface, without significantly compromising spin transport from the magnetic material across the TiO x to the TI surface states. First, it is demonstrated that in Bi 2 Te 3 /TiO x /Ni 80 Fe 20 heterostructures, TiO x provides an e...

Insights into the Stability and Surface Termination of Topological Semimetal NbAs2

“…Topological materials, a novel class of quantum matter, are distinguished by the robustness of their surface states against non-magnetic perturbations, a consequence of their non-trivial topology. [1] These materials, particularly topological insulators, [2][3][4] semimetals, [5][6][7][8][9] and superconductors, [10][11][12][13] have generated a significant research interest due to their potential implications for quantum computing [14] and spintronics. [15] The exotic phenomena exhibited by these materials, such as the quantum anomalous Hall effect [16][17][18] and Majorana fermions, [19][20][21][22] defy traditional paradigms, requiring innovative theoretical and experimental approaches for their comprehensive understanding.…”

Nanostructure, magnetism, and transport behaviors of magnetic and topological thin films and heterostructures

“…However, it may be useful to mitigate this mixed interface formation by introducing a spacer layer such as Ag, or Ti. [38], [55], [56], [57], [58] More studies should be conducted about whether the spin-pumping effect is enhanced by the presence of an additional AFM phases at the interface of TI/FM heterostructures. While this work focused on the FM/AFM exchange coupling between permalloy and the interfacial AFM phase formed at the interface with Sb 2 Te 3 there has been other interesting research directions focused on AFM/TI coupled interactions in literature.…”

“…Therefore, there have been multiple efforts to suppress these chemical interactions using spacer layers, such as Ag, TiO x , Cu, Al, or Ti. [38], [55], [56], [57], [58] Another challenge for TI/FM SOT-based devices is associated with the use of a Since magnetic TIs (MTIs), a sub-class of TI materials with magnetic order, promise zero dissipation transport via the quantum spin-Hall effect (QSHE) and the quantum anomalous…”