Monolayer WSe2_2 substitutionally doped with vanadium was reported in 2020 to show long-range ferromagnetic order persisting above room temperature, with gate-tunable magnetic domains observed by magnetic force microscopy — a putative two-dimensional dilute magnetic semiconductor. The microscopic origin of this magnetism remains undetermined and is now explicitly contested. One body of work — density-functional theory, photoemission, transport, and optical spectroscopy, largely from the original group — supports carrier-mediated (Zener- or RKKY-type) exchange among substitutional V moments mediated by itinerant spin-polarized holes. A 2025 independent re-examination of molecular-beam-epitaxy-grown monolayers found no ferromagnetism in low-defect V-doped WSe2_2 at any doping up to 35%, quantified dopant clustering, and attributed all reported room-temperature ferromagnetism in WSe2_2 to selenium vacancies. This problem asks for a defect-controlled microscopic account of the magnetic state: which mechanism produces the reported order, together with a quantitative model reproducing the observed non-monotonic gate-bias dependence and doping dependence of TcT_c; the magnetic roles of the distinct V chemical forms seen by electron microscopy; the nature of the multiphase, spin-glass-like MM–TT response; and quantitative moment, spin-polarization, and exchange-splitting measurements on monolayer samples.

Background

A dilute magnetic semiconductor (DMS) is a semiconductor into which a small concentration of magnetic atoms is introduced so that carrier transport and magnetic order couple — and, ideally, so that the magnetism can be tuned by an electrostatic gate. The canonical example, Mn-doped GaAs, shows gate-modulated ferromagnetism but orders only far below room temperature; atomically thin intrinsic van der Waals magnets such as CrI3_3 and CrGeTe3_3 lose magnetic order below roughly 60 K; and metallic monolayer magnets such as VSe2_2 can order above room temperature but lack a gate-tunable carrier density. A semiconducting, gate-tunable, room-temperature two-dimensional DMS has therefore been a standing target of the field.

WSe2_2 is a semiconducting transition-metal dichalcogenide (TMD); its monolayer retains a sizeable band gap and strong spin–orbit coupling. In 2020, Yun and co-workers reported that replacing 0.1–2% of the W atoms with vanadium during chemical-vapor-deposition growth produced monolayers displaying magnetic domains in magnetic force microscopy (MFM — a scanned-probe technique that senses a sample's stray field with a magnetized tip) up to about 360 K, with a Curie temperature TcT_c that decreased with doping (≈360, 270, and 220 K at 0.1%, 0.5%, and 2% V), a transistor on/off ratio near 10510^{5} (preserving semiconducting behavior), and a non-monotonic modulation of the domain contrast by back-gate bias (near-zero at −10 V, maximal near +15 V, decreasing above). Atomic-resolution scanning transmission electron microscopy (STEM) showed isolated substitutional V atoms (V–V separations of a few nm at 0.1% doping) coexisting with two local chemical forms, VSe and VSe2_2-like species. The authors suggested — but did not establish — a carrier-mediated origin: Ruderman–Kittel–Kasuya–Yosida (RKKY) indirect exchange or Zener-type exchange, in which spin-polarized free holes align the V moments. They also reported a complicated, spatially variable magnetization-versus-temperature (MM–TT) response suggesting multiphase transitions possibly including a spin-glass component (a frozen, disordered magnetic state), ambient sensitivity of the domains partly mitigated by Al2_2O3_3 passivation, and the fact that monolayer moments fall below the sensitivity of bulk magnetometers such as those based on the superconducting quantum interference device (SQUID).

Later work complicated rather than settled this picture. Theory from the original group supports hole-mediated order at low V densities, while independent calculations find V-doped WSe2_2 ferromagnetic only at far higher substitution levels and show that dopant clustering — which is energetically favored — strongly suppresses the exchange. Most importantly, a 2025 independent study of molecular-beam-epitaxy monolayers observed no ferromagnetism in low-defect V-doped WSe2_2 up to 35% substitution and concluded that all reported room-temperature ferromagnetism in WSe2_2, doped or undoped, is caused by selenium vacancies. The microscopic origin of the reported magnetism is thus an open and actively contested question.

Problem Statement

Determine the microscopic origin of the reported long-range ferromagnetic order at room temperature in substitutionally vanadium-doped monolayer WSe2_2. A complete answer must establish whether the magnetism is intrinsic to substitutional V moments coupled by itinerant spin-polarized holes through Zener- or RKKY-type indirect exchange, or whether it originates instead in dopant clustering or in moments induced by selenium vacancies — and must provide a quantitative microscopic account that reproduces the reported phenomenology: the non-monotonic dependence of the magnetic response on gate bias, the doping dependence of TcT_c (≈360, 270, and 220 K at 0.1%, 0.5%, and 2% V), and the complex, spatially variable MM–TT behavior including any spin-glass-like phases. It must further address the magnetic roles of the distinct local chemical forms of vanadium resolved by STEM (substitutional VSe versus VSe2_2-like species), the stability and reproducibility of the magnetic domains under ambient exposure, and quantitative determination of the magnetic moment per V atom, the spin polarization, the exchange splitting, and the carrier–spin coupling strength, predicted from a microscopic model and accompanied by identification of the monolayer measurement that would test each. These facets jointly constitute one objective, and none is independently sufficient: a defect-controlled, quantitatively verified microscopic account of the magnetic state of monolayer V:WSe2_2 that reconciles the conflicting experimental record, including the 2025 finding that low-defect doped monolayers show no ferromagnetism while selenium-vacancy density tracks the observed magnetism. "Quantitatively verified" here denotes that the account reproduces the reported phenomenology enumerated above — the non-monotonic dependence of the magnetic response on gate bias, the stated TcT_c values (≈360, 270, and 220 K at 0.1%, 0.5%, and 2% V), and the complex, spatially variable MM–TT behavior.

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