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1. A generic dual d-band model for interlayer ferromagnetic coupling in a transition-metal doped MnBi ₂ Te ₄ family of materials

   https://doi.org/10.1039/D2NR03283J  

   Zhang, Huisheng; Zhang, Jingjing; Zhang, Yaling; Yang, Wenjia; Wang, Yingying; Xu, Xiaohong; Liu, Feng (September 2022, Nanoscale)

   Realization of ferromagnetic (FM) interlayer coupling in magnetic topological insulators (TIs) of the MnBi 2 Te 4 family of materials (MBTs) may pave the way for realizing the high-temperature quantum anomalous Hall effect (high- T QAHE). Here we propose a generic dual d-band (DDB) model to elucidate the energy difference (Δ E = E AFM − E FM ) between the AFM and FM coupling in transition-metal (TM)-doped MBTs, where the valence of TMs splits into d-t 2g and d-e g sub-bands. Remarkably, the DDB shows that Δ E is universally determined by the relative position of the dopant (X) and Mn d-e g / t 2g bands, . If Δ E d > 0, then Δ E > 0 and the desired FM coupling is favored. This surprisingly simple rule is confirmed by first-principles calculations of hole-type 3d and 4d TM dopants. Significantly, by applying the DDB model, we predict the high- T QAHE in the V-doped Mn 2 Bi 2 Te 5 , where the Curie temperature is enhanced by doubling of the MnTe layer, while the topological order mitigated by doping can be restored by strain. 

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2. High Curie temperature ferromagnetic structures of (Sb2Te3)1−x(MnSb2Te4)x with x = 0.7–0.8

   https://doi.org/10.1038/s41598-023-34585-y  

   Levy, Ido; Forrester, Candice; Ding, Xiaxin; Testelin, Christophe; Krusin-Elbaum, Lia; Tamargo, Maria C. (December 2023, Scientific Reports)

   Abstract Magnetic topological materials are promising for realizing novel quantum physical phenomena. Among these, bulk Mn-rich MnSb 2 Te 4 is ferromagnetic due to Mn Sb antisites and has relatively high Curie temperatures (T C ), which is attractive for technological applications. We have previously reported the growth of materials with the formula (Sb 2 Te 3 ) 1−x (MnSb 2 Te 4 ) x , where x varies between 0 and 1. Here we report on their magnetic and transport properties. We show that the samples are divided into three groups based on the value of x (or the percent septuple layers within the crystals) and their corresponding T C values. Samples that contain x < 0.7 or x > 0.9 have a single T C value of 15–20 K and 20–30 K, respectively, while samples with 0.7 < x < 0.8 exhibit two T C values, one (T C1 ) at ~ 25 K and the second (T C2 ) reaching values above 80 K, almost twice as high as any reported value to date for these types of materials. Structural analysis shows that samples with 0.7 < x < 0.8 have large regions of only SLs, while other regions have isolated QLs embedded within the SL lattice. We propose that the SL regions give rise to a T C1 of ~ 20 to 30 K, and regions with isolated QLs are responsible for the higher T C2 values. Our results have important implications for the design of magnetic topological materials having enhanced properties. 

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3. Alloying of Mn with Bi‐Rich Surfaces of Bi ₂ Te ₃ by Topotactic Reaction

   https://doi.org/10.1002/smll.202504498  

   Khatun, Salma; Maity, Nikhilesh; Lisenkov, Sergey; Ponomareva, Inna; Batzill, Matthias (October 2025, Small)

   Abstract Interfacing topological insulators (TI) with magnetic materials enables accessing quantum effects for advanced devices. The synthesis of such heterostructures faces challenges due to interlaying mixing and the often‐complex multicomponent materials required to combine the desired properties. An alternative synthesis to direct growth is the modification of 2D materials by topotactic reactions to introduce new functionalities into pre‐formed single or few‐component 2D sheets. Here, the self‐formation of bismuthene (a bilayer of Bi; Bi₂) is utilized by thermal decomposition of Bi₂Te₃as a platform to create novel 2D overlayers on the TI‐ substrate. Specifically, the Bi₂layer is modified by reacting it with vapor deposited Mn in an attempt to induce magnetic properties. Scanning tunneling microscopy indicates that the Mn modified surface remains in a planar 2D layer, indicating the formation of an ordered Mn‐rich surface layer. Density functional theory (DFT) is used to develop models of both the Bi‐rich Bi₂Te₃surface as well as their subsequent Mn‐modified structure. The DFT models indicate the possibility of magnetic ordering of the high spin Mn²⁺ions. The successful synthesis of planar MnBi alloys on a van der Waals material illustrates topotactic reactions as an alternative for creating novel layered heterostructures. 

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4. Mn substitution in the topological metal Zr ₂ Te ₂ P

   https://doi.org/10.1088/1361-648X/ac9770  

   Oladehin, O; Feng, K; Haddock, J W; Galeano-Cabral, J; Wei, K; Xin, Y; Latturner, S E; Baumbach, R E (October 2022, Journal of Physics: Condensed Matter)

   Abstract Results are reported for Mn intercalated Zr 2 Te 2 P, where x-ray diffraction , energy dispersive spectroscopy, and transmission electron microscopy measurements reveal that the van der Waals bonded Te–Te layers are partially filled by Zr and Mn ions. This leads to the chemical formulas Zr 0.07 Zr 2 Te 2 P and Mn 0.06 Zr 0.03 Zr 2 Te 2 P for the parent and substituted compounds, respectively. The impact of the Mn ions is seen in the anisotropic magnetic susceptibility, where Curie–Weiss fits to the data indicate that the Mn ions are in the divalent state. Heat capacity and electrical transport measurements reveal metallic behavior, but the electronic coefficient of the heat capacity ( γ Mn ≈ 36.6 mJ (mol·K 2 ) −1 ) is enhanced by comparison to that of the parent compound. Magnetic ordering is seen at T M ≈ 4  K, where heat capacity measurements additionally show that the phase transition is broad, likely due to the disordered Mn distribution. This transition also strongly reduces the electronic scattering seen in the normalized electrical resistance. These results show that Mn substitution simultaneously introduces magnetic interactions and tunes the electronic state, which improves prospects for inducing novel behavior in Zr 2 Te 2 P and the broader family of ternary tetradymites. 

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5. Te Vacancies Induced Magnetic Domains and Domain Wall Stabilization on Fe ₃ GeTe ₂ Surfaces

   https://doi.org/10.1002/adfm.77224  

   Baral, Dinesh; Fu, ZhuangEn; Chen, Hua; Tian, Jifa; Chien, TeYu (July 2026, Advanced Functional Materials)

   ABSTRACT Fe₃GeTe₂(FGT) is a van der Waals (vdW) ferromagnetic (FM) metal. When the thickness is around tens of nm, it exhibits thickness, temperature, and magnetic field dependent magnetic phases, including skyrmions, magnetic stripes, and labyrinth magnetic domains. These magnetic phases can be further influenced by Fe defects, interfacial Dzyaloshinskii–Moriya interaction (DMI), and strain. Here, the influences of Te vacancies on the magnetic domains on the surfaces of FGT are reported. The Te vacancies are introduced during the exfoliation process and are determined from the atomic resolution scanning tunneling microscopy (STM) images. Te vacancies are found to be responsible for inducing magnetic domains with opposite magnetic moments on the otherwise ferromagnetic surface. Magnetic domain expands upon increasing the temperature, and the Te vacancies serve to stabilize magnetic domain boundaries during the expansion of the magnetic domain sizes. Also, a theoretical model describing the role of Te vacancies to reduce the domain wall energy and hence acting as pinning sites to form the labyrinth like magnetic domain has been presented. The results presented here point out that the Te vacancies may play a significant role in altering magnetic phases. 

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