Surface‐Driven Evolution of the Anomalous Hall Effect in Magnetic Topological Insulator MnBi₂Te₄ Thin Films

Abstract

Understanding the effects of the interfacial modification to the functional properties of magnetic topological insulator thin films is crucial for developing novel technological applications from spintronics to quantum computing. Here, a large electronic and magnetic response is reported to be induced in the intrinsic magnetic topological insulator MnBi 2 Te 4 by controlling the propagation of surface oxidation. It is shown that the formation of the surface oxide layer is confined to the top 1-2 unit cells but drives large changes in the overall magnetic response. Specifically, a dramatic reversal of the sign of the anomalous Hall effect is observed to be driven by finite thickness magnetism, which indicates that the film splits into distinct magnetic layers each with a unique electronic signature. These data reveal a delicate dependence of the overall magnetic and electronic response of MnBi 2 Te 4 on the stoichiometry of the top layers. This study suggests that perturbations resulting from surface oxidation may play a non-trivial role in the stabilization of the quantum anomalous Hall effect in this system and that understanding targeted modifications to the surface may open new routes for engineering novel topological and magnetic responses in this fascinating material.

Fabrication-induced even-odd discrepancy of magnetotransport in few-layer MnBi2Te4

“…In order to figure out the reason for the color change and to exclude any artificial factor that may contribute to our observation, such as the transport electrodes, fabrication conditions, and imaging parameters etc., we conducted thorough control experiments on many few-layer flakes and compared O c changes under different conditions (see supplementary section D for details). To mitigate the potential interferences from extrinsic effects, such as thermal cycling, environmental doping, and aging effect, O c was obtained immediately after surface treatment in a glovebox 36 , 37 , 48 , 49 . Of the many relevant factors, we notice that the contact with PMMA plays the most crucial role on the reduction of O c , a factor that was rarely noticed in previous studies of 2D materials.…”

High entropy ceramics for applications in extreme environments

“…As an example, MnBi 2 Te 4 can exhibit the quantum anomalous Hall effect [145] subject to its highly sensitive to small degrees of doping and stacking order [146]. However, the resistance of materials such as these to even exposure to oxygen can destroy or alter the properties they exhibit [147]. In fact, superconductivity has been observed in high entropy tellurides with unconventional robustness to extreme pressures [142]-a strong indicator towards the functional stability of chalcogenides synthesized by this approach.…”

Topical Review of Quantum Materials and Heterostructures Studied by Polarized Neutron Reflectometry

“…[103] Bulk MnBi 2 Te 4 is perfectly compensated, while PNR measurements show a vanishingly small magnetization in 10 nm-thick films of MnBi 2 Te 4 . [118] It is expected that sufficiently thin films of MnBi 2 Te 4 , however, should lead to an uncompensated layer appearing that may be detectable with PNR. A major challenge, however, is the complex oxide layer that naturally forms at the ambient exposed interface.…”

“…A major challenge, however, is the complex oxide layer that naturally forms at the ambient exposed interface. [118] Neutron reflectometry was used to characterize the thickness of this oxide, and importantly, the charge transfer associated with the oxide layer was shown to affect the anomalous Hall effect of the underlying TI structure. [118] A practical drawback with some of the existing platforms of magnetic proximity effects in TIs is air sensitivity, or chemical incompatibility with existing industrial processes.…”

“…[118] Neutron reflectometry was used to characterize the thickness of this oxide, and importantly, the charge transfer associated with the oxide layer was shown to affect the anomalous Hall effect of the underlying TI structure. [118] A practical drawback with some of the existing platforms of magnetic proximity effects in TIs is air sensitivity, or chemical incompatibility with existing industrial processes. For this reason, a new stream of research has emerged which studies heterostructures of TIs with common spintronic materials, already used industrially, with high Curie temperatures and wellunderstood oxidation behavior.…”