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1. Magnetic memory driven by topological insulators

   https://doi.org/10.1038/s41467-021-26478-3  

   Wu, Hao; Chen, Aitian; Zhang, Peng; He, Haoran; Nance, John; Guo, Chenyang; Sasaki, Julian; Shirokura, Takanori; Hai, Pham Nam; Fang, Bin; et al (December 2021, Nature Communications)

   Abstract Giant spin-orbit torque (SOT) from topological insulators (TIs) provides an energy efficient writing method for magnetic memory, which, however, is still premature for practical applications due to the challenge of the integration with magnetic tunnel junctions (MTJs). Here, we demonstrate a functional TI-MTJ device that could become the core element of the future energy-efficient spintronic devices, such as SOT-based magnetic random-access memory (SOT-MRAM). The state-of-the-art tunneling magnetoresistance (TMR) ratio of 102% and the ultralow switching current density of 1.2 × 10 5  A cm −2 have been simultaneously achieved in the TI-MTJ device at room temperature, laying down the foundation for TI-driven SOT-MRAM. The charge-spin conversion efficiency θ SH in TIs is quantified by both the SOT-induced shift of the magnetic switching field ( θ SH  = 1.59) and the SOT-induced ferromagnetic resonance (ST-FMR) ( θ SH  = 1.02), which is one order of magnitude larger than that in conventional heavy metals. These results inspire a revolution of SOT-MRAM from classical to quantum materials, with great potential to further reduce the energy consumption. 

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2. Giant Hall Switching by Surface‐State‐Mediated Spin‐Orbit Torque in a Hard Ferromagnetic Topological Insulator

   https://doi.org/10.1002/adma.202406772  

   Tai, Lixuan; He, Haoran; Chong, Su Kong; Zhang, Huairuo; Huang, Hanshen; Qiu, Gang; Ren, Yuxing; Li, Yaochen; Yang, Hung‐Yu; Yang, Ting‐Hsun; et al (November 2024, Advanced Materials)

   Abstract Topological insulators (TI) and magnetic topological insulators (MTI) can apply highly efficient spin‐orbit torque (SOT) and manipulate the magnetization with their unique topological surface states (TSS) with ultrahigh efficiency. Here, efficient SOT switching of a hard MTI, V‐doped (Bi,Sb)₂Te₃(VBST), with a large coercive field that can prevent the influence of an external magnetic field, is demonstrated. A giant switched anomalous Hall resistance of 9.2 kΩ is realized, among the largest of all SOT systems, which makes the Hall channel a good readout and eliminates the need to fabricate complicated magnetic tunnel junction (MTJ) structures. The SOT switching current density can be reduced to 2.8 × 10⁵ A cm⁻², indicating its high efficiency. Moreover, as the Fermi level is moved away from the Dirac point by both gate and composition tuning, VBST exhibits a transition from edge‐state‐mediated to surface‐state‐mediated transport, thus enhancing the SOT effective field to (1.56 ± 0.12) × 10⁻⁶ T A⁻¹ cm²and the interfacial charge‐to‐spin conversion efficiency to 3.9 ± 0.3 nm⁻¹. The findings establish VBST as an extraordinary candidate for energy‐efficient magnetic memory devices. 

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3. Layer‐Dependent Antiferromagnetic Chern and Axion Insulating States in UOTe

   https://doi.org/10.1002/advs.202510247  

   Mardanya, Sougata; Ghosh, Barun; Liu, Mengke; Broyles, Christopher; Ahn, Junyeong; Sun, Kai; Hoffman, Jennifer E; Ran, Sheng; Bansil, Arun; Xu, Su‐Yang; et al (April 2026, Advanced Science)

   ABSTRACT Magnetic topological insulators have received significant interest due to their dissipationless edge states, which promise advances in energy‐efficient electronic transport. However, the magnetic topological insulator state has typically been found in ferromagnets (FMs) that suffer from low magnetic ordering temperatures and stray fields. Identifying an antiferromagnetic topological insulator that exhibits the quantum anomalous Hall effect (QAHE) with a relatively high Néel temperature has been a longstanding challenge. Here, we focus on the recently discovered van der Waals (vdW) antiferromagnet (AFM) UOTe, which not only features a high Néel temperature (≈ 150K) but also exhibits intriguing Kondo interaction and topological characteristics. Our systematic analysis of the layer‐dependent topological phases based on ab initio computations predicts the two‐layer UOTe film to be an ideal 2D AFM Chern insulator in which the Hall conductivity is quantized with a fully compensated spin magnetization. By applying an in‐plane strain or electric field, we show how the itinerancy of U‐5f electrons can be manipulated to trigger a transition between the nontrivial (C  =  1) and trivial (C  =  0) phases. Interestingly, the three‐layer UOTe film is found to have zero charge conductance but it hosts a quantized spin Hall conductivity (SHC) with finite magneto‐electric coupling, suggesting the presence of an axion insulator‐like state. The unique magnetic structure of UOTe supports a layer‐tunable topology in which films with an odd number of layers are axion‐like insulators, while films with an even number of layers are Chern insulators, and the bulk material is a Dirac semimetal. Our study offers a new intrinsic AFM materials platform for realizing correlated topological phases for next‐generation spintronics applications and fundamental science studies. 

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4. Enhanced ferromagnetism in monolayer Cr ₂ Te ₃ via topological insulator coupling

   https://doi.org/10.1088/1361-6633/add9c5  

   Ou, Yunbo; Mirzhalilov, Murod; Nemes, Norbert M; Martinez, Jose L; Rocci, Mirko; Duong, Alexander; Akey, Austin; Foucher, Alexandre C; Ge, Wenbo; Suri, Dhavala; et al (May 2025, Reports on Progress in Physics)

   Abstract Exchange-coupled interfaces are pivotal in exploiting two-dimensional (2D) ferromagnetism. Due to the extraordinary correlations among charge, spin, orbital and lattice degrees of freedom, layered magnetic transition metal chalcogenides (TMCs) bode well for exotic topological phenomena. Here we report the realization of wafer-scale Cr₂Te₃down to monolayer (ML) on insulating SrTiO₃(111) and/or Al₂O₃(001) substrates using molecular beam epitaxy. Robust ferromagnetism persists in the 2D limit. In particular, the Curie temperatureT_Cof 2 ML Cr₂Te₃increases from 100 K to ∼120 K when proximitized to topological insulator (TI) (Bi,Sb)₂Te₃, with substantially boosted magnetization as observed via polarized neutron reflectometry. Our experiments and theory strongly indicate that the Bloembergen–Rowland interaction is likely universal underlyingT_Cenhancement in TI-coupled magnetic heterostructures. The topological-surface-enhanced magnetism in 2D TMC enables further exchange coupling physics and quantum hybrid studies, including paving the way to realize interface-modulated topological electronics. 

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5. Spin-resolved topology and partial axion angles in three-dimensional insulators

   https://doi.org/10.1038/s41467-024-44762-w  

   Lin, Kuan-Sen; Palumbo, Giandomenico; Guo, Zhaopeng; Hwang, Yoonseok; Blackburn, Jeremy; Shoemaker, Daniel P.; Mahmood, Fahad; Wang, Zhijun; Fiete, Gregory A.; Wieder, Benjamin J.; et al (December 2024, Nature Communications)

   Abstract Symmetry-protected topological crystalline insulators (TCIs) have primarily been characterized by their gapless boundary states. However, in time-reversal- ($${{{{{{{\mathcal{T}}}}}}}}$$ $T$ -) invariant (helical) 3D TCIs—termed higher-order TCIs (HOTIs)—the boundary signatures can manifest as a sample-dependent network of 1D hinge states. We here introduce nested spin-resolved Wilson loops and layer constructions as tools to characterize the intrinsic bulk topological properties of spinful 3D insulators. We discover that helical HOTIs realize one of three spin-resolved phases with distinct responses that are quantitatively robust to large deformations of the bulk spin-orbital texture: 3D quantum spin Hall insulators (QSHIs), “spin-Weyl” semimetals, and$${{{{{{{\mathcal{T}}}}}}}}$$ $T$ -doubled axion insulator (T-DAXI) states with nontrivial partial axion angles indicative of a 3D spin-magnetoelectric bulk response and half-quantized 2D TI surface states originating from a partial parity anomaly. Using ab-initio calculations, we demonstrate thatβ-MoTe₂realizes a spin-Weyl state and thatα-BiBr hosts both 3D QSHI and T-DAXI regimes. 

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