Janus MnSeTe: 2D Magnetism & Skyrmions

• Janus MnSeTe is a 2D magnet with a Mn layer asymmetrically sandwiched by Se and Te, breaking inversion symmetry to enable robust Dzyaloshinskii–Moriya interaction and skyrmion formation.
• It exhibits tunable electronic properties with an indirect band gap of ~1.05 eV and a significant spin-splitting of ~1.01 eV under spin–orbit coupling, modulated by biaxial strain.
• Higher-order exchange interactions in MnSeTe create high energy barriers (~330 meV) for skyrmion stability, highlighting its potential for low-power, tunable spintronic devices.

Janus MnSeTe is a two-dimensional van der Waals magnet distinguished by its lack of inversion symmetry, arising from the presence of two chemically distinct chalcogen atoms (selenium and tellurium) sandwiching a manganese layer. This structural asymmetry imparts MnSeTe with unconventional magnetic phenomena, pronounced Dzyaloshinskii–Moriya interaction (DMI), and robust skyrmion formation, positioning the material at the forefront of tunable 2D spintronics and nanomagnetism platforms.

1. Atomic and Crystallographic Structure

Janus MnSeTe adopts a bilayer atomic configuration where Mn atoms are threefold coordinated to Se on one side and Te on the opposing side, resulting in pronounced out-of-plane buckling. The typical buckling heights are approximately 1.01 Å (Se–Mn) and 0.72 Å (Te–Mn), with an in-plane lattice constant near 4.40 Å (Sattar et al., 2022). The difference in chemical composition across the vertical direction generates a substantial asymmetrical potential, breaking both inversion and time-reversal symmetry at the lattice level. Bond angles between the Mn–chalcogen–Mn coupling deviate on each face (about 32° versus 67°), which influences the electronic distribution and local orbital environments. The absence of inversion symmetry is critical to activating DMI and spin-splitting phenomena.

2. Electronic Properties: Band Structure and Spin-Splitting

Janus MnSeTe exhibits an indirect semiconductor band gap, calculated to be ~1.05 eV (in DFT without spin–orbit coupling, SOC), with the valence band maximum and conduction band minimum occurring at disparate k-points in the Brillouin zone (Sattar et al., 2022). The valence states are dominated by chalcogen p-orbitals from both Se and Te; conduction states primarily involve Mn d-orbitals. The band gap is highly tunable via biaxial tensile or compressive strain (±4%), allowing monotonic increases with tensile strain and decreases with compression, enabling energy gap engineering for optoelectronic applications.

With SOC included, the lack of inversion symmetry induces substantial spin-splitting: the valence band exhibits a splitting of about 1.01 eV (Sattar et al., 2022). The SOC Hamiltonian underpinning this phenomenon is:

$$H_{\mathrm{SO}} = \lambda\, (\mathbf{L} \cdot \mathbf{S}) = \lambda \left( L_z S_z + \frac{1}{2}L_+S_- + \frac{1}{2}L_-S_+ \right)$$

This manifests as a distinct spin-split band structure despite the globally compensated antiferromagnetic order (zero net moment), which can enable electrically controlled spin–polarized or valley-polarized charge transport.

3. Magnetic Phenomena: DMI, Skyrmions, and Higher-Order Exchange

The broken symmetry and strong SOC from the heavy Te atom yield a large DMI that is central to MnSeTe’s magnetic behavior. The in-plane DMI amplitude ($d_{\parallel}$) is calculated to be 2.14 meV (Liang et al., 2019), comparable to FM/HM heterostructures but achieved within a monolayer. This DMI competes with ferromagnetic exchange, and the spin Hamiltonian of MnSeTe includes:

$$H = -\sum_{ij} J_{ij} (\mathbf{m}_i \cdot \mathbf{m}_j) - \sum_{ij} \mathbf{D}_{ij} \cdot (\mathbf{m}_i \times \mathbf{m}_j) - K_{u} \sum_{i} (m_i^z)^2 - \sum_{i} \mu (\mathbf{m}_i \cdot \mathbf{B}) + H_{\textrm{HOI}}$$

where $H_{\textrm{HOI}}$ incorporates higher-order exchange interactions (HOI), including biquadratic and quartet terms:

$$H_{\textrm{HOI}} = -B_1 \sum_{\langle ij\rangle} (\mathbf{m}_i \cdot \mathbf{m}_j)^2 -2Y_1 \sum_{\langle ijk\rangle} (\mathbf{m}_i \cdot \mathbf{m}_j)(\mathbf{m}_j \cdot \mathbf{m}_k) -K_1 \sum_{\langle ijkl\rangle} \left[ (\mathbf{m}_i \cdot \mathbf{m}_j)(\mathbf{m}_k \cdot \mathbf{m}_l) + (\mathbf{m}_i \cdot \mathbf{m}_l)(\mathbf{m}_j \cdot \mathbf{m}_k) - (\mathbf{m}_i \cdot \mathbf{m}_k)(\mathbf{m}_j \cdot \mathbf{m}_l) \right]$$

(Arya et al., 12 Sep 2025)

Such terms are found to dramatically modify the mechanism of skyrmion collapse—giving rise to a novel “ferric transition” where a quasi–ferrimagnetic intermediate state mediates the topological change. In contrast to radial or chimera transitions, the Bloch point (where the topological charge jumps from $Q = -1$ to $Q = 0$) is shifted by HOI, while the global energy barrier for collapse remains determined by DMI (~330 meV), which is among the highest observed in intrinsic 2D magnets (Arya et al., 12 Sep 2025).

4. Skyrmion Formation, Stability, and Tunability

Janus MnSeTe supports intrinsic Néel-type skyrmions at zero magnetic field, stabilized by strong DMI and SOC (Yuan et al., 2019). The skyrmion diameter is approximately 41 nm under zero field and can be reduced to sub-10 nm by application of a positive out-of-plane field; conversely, negative fields cause expansion and eventual annihilation. The skyrmion number (topological index, $n$) is:

$$n = \frac{1}{4\pi} \int \mathbf{m} \cdot (\partial_x \mathbf{m} \times \partial_y \mathbf{m})\, dx\, dy$$

With $n = -1$, these skyrmions are topologically protected. Micromagnetic simulations indicate that skyrmion states persist up to $T \sim 50$ K, above which thermal fluctuations induce disorder and blurring (Liang et al., 2019). Skyrmion energy barriers are exceptionally high (~330 meV), conferring strong thermal stability (Arya et al., 12 Sep 2025). The stability and tunability of skyrmion size/shape—achieved via external field and strain—offer dynamic control for device integration.

5. Comparative Analysis with Related Janus Mn Dichalcogenides

Table 1: Comparison of magnetic characteristics in MnSeTe and MnSTe (Liang et al., 2019)

Property	MnSeTe	MnSTe
$d_{\parallel}$ (meV)	2.14	2.63
DMI/Exchange ratio	~0.16	~0.25
Skyrmion onset field	~0.05 T	~1.4–1.8 T
Domain size	Larger	Smaller

MnSTe, with a greater DMI/exchange ratio, requires higher fields for skyrmion formation and exhibits smaller domain sizes. Thus, magnetic properties are highly tunable across Janus platforms by controlling chalcogen composition and associated SOC effects.

6. Potential Applications: Spintronics and Functional Materials

Janus MnSeTe’s properties—high DMI, large skyrmion stability barriers, tunable semiconductor gap, and strong spin-splitting—render it a promising candidate for several device paradigms:

• Spintronic memory: Skyrmion-based racetrack memory, exploiting the ability to nucleate, control, and annihilate skyrmions with low-power magnetic fields (Liang et al., 2019, Yuan et al., 2019).
• Energy-efficient logic: Use of stable skyrmions as carriers for logic gating and information transfer, achieving ultra-dense packing and low switching energy (Yuan et al., 2019).
• Flexible electronics: Band gap and spin-splitting tunable by strain, supporting adaptable photo-sensitive or field-tunable platforms (Sattar et al., 2022).
• AFM spintronics and valleytronics: Staggered moments and SOC-induced band splitting open pathways for field-free switching, THz speed operation, and non-volatile memory design (Sattar et al., 2022).

A plausible implication is that, given the role of Se in magnetic anisotropy and the SOC enhancement with Te, alloying strategies within Mn-chalcogen families could further optimize device performance (Huang et al., 9 Jun 2024).

7. Current Challenges and Future Research Directions

The thermal stability limit (skyrmion persistence only below $T \sim 50$ K), while offering robust nanoscale order, restricts immediate applications at room temperature (Liang et al., 2019). Recent progress in MnSeI and MnSeCl systems—which show Curie temperatures above and near room temperature and similar mechanisms of magnetic anisotropy—suggests that tuning Te/Se substitution or exploring Janus variants with heavier halogens may yield MnSeTe derivatives with higher operational windows (Huang et al., 9 Jun 2024).

The discovery of HOI-driven ferric topological transitions (Arya et al., 12 Sep 2025) introduces new complexity in skyrmion dynamics, necessitating further experimental validation and exploration of its impact on device scaling, switching pathways, and robustness under non-ideal conditions.

Summary

Janus MnSeTe is a structurally and electronically asymmetric 2D magnet characterized by strong DMI, robust skyrmion formation, and rich tunable electronic and magnetic properties. Its unique combination of intrinsic inversion symmetry breaking, large magnetic energy barriers, and dynamic control over topological spin textures positions it at the center of emerging research in 2D skyrmionics, spintronics, and flexible nanomagnetism, with future applicability hinging on continued advances in chemical engineering, thermal stabilization, and higher-order exchange phenomena.