Vanadium triiodide

VI₃

Also called vanadium(III) iodide

van der Waals crystal magnet

The vanadium counterpart of CrI₃: the same honeycomb layer, but each vanadium ion carries two d electrons instead of chromium’s three – a spin of 1 rather than 3/2 and, calculations suggest, an orbital moment that is not quenched. The result is a hard ferromagnet below about 50 K, with a coercive field of 9.1 kOe at 2 K and an easy axis tilted about 40° away from the layer normal. It is a Mott insulator with an optical gap of 0.6–0.67 eV, exfoliates to a few layers, and is predicted to stay a ferromagnet as a monolayer. Even its crystal structure is still argued over.

Data sheet

Show all 7 entriesHide the data sheet

Kind of sheet: van der Waals crystal
Peels off a layered crystal, one sheet at a time
Behaves as: magnet
Band gap: Insulating: optical gap 0.6–0.67 eV in bulk crystals, probably a Mott insulator

In colour: this family, 0.6–0.67 eV. In grey: the other 41 families on the catalogue’s chart, each at the middle of its range. The dashed line marks bulk silicon, 1.12 eV.
Thickness: ~0.66 nm per layer
Structure: V³⁺ ions on a honeycomb lattice, each inside an octahedron of iodide ions, as in CrI₃. How the layers stack is disputed: single-crystal studies find the rhombohedral BiI₃ type (R-3) at room temperature, turning monoclinic near 79 K and triclinic at 32 K – the reverse of the chromium trihalides, whose low-temperature phase is the more symmetric one; a powder study proposed a trigonal P-31c structure instead; and one group reports the opposite sequence, monoclinic above and rhombohedral below 79 K
Stability: Sensitive to air and moisture, like CrI₃: X-ray diffraction from an uncovered crystal fades with a time constant of 15–20 hours in air, so thin flakes are handled in a glovebox and encapsulated.
First made: 2019 – exfoliated down to a few layers by Tian and colleagues; ferromagnetism in bulk crystals reported the same year by Kong and colleagues and by Son and colleagues

Compare with other materials

Key properties

Ferromagnetic below 49–50 K in bulk crystals; magneto-optical Kerr imaging shows domains that an applied field moves
A hard magnet: a coercive field of 9.1 kOe at 2 K
The easy axis is tilted about 40° from the c axis, closely tied to the crystal structure
Structural transitions near 79 K and at 32 K, the lower one probably tied to a change in the magnetic structure – signs of strong coupling between magnetism and lattice
Optical gap of 0.6–0.67 eV and a very high resistance: probably a Mott insulator
Calculations predict a monolayer Ising ferromagnet ordering near 70 K, and 90–110 K under 2.5–5% tensile strain

How it is made

Bulk single crystals, used for most measurements
Mechanical exfoliation down to a few layers, made easy by weak binding between the layers

Uses, and how close they are

Model system for hard, orbitally driven magnetism in van der Waals layerslab

Readiness runs lab → prototype → pilot → deployed.

Open problems

What is the crystal structure at each temperature, and why do studies disagree?
Does a single layer order ferromagnetically, and at the temperature calculations predict?
How large is the orbital moment, and how does it set the tilted easy axis and the large coercive field?

All 256 open problems on Flatland, by theme

Going deeper

Short notes for specialists. Choose a lens in the header and yours comes first.

For theoreticians · your lens

A d² ion in a trigonal crystal field: calculations find a ground state with an unquenched orbital moment (Lz = −1), which gives a strong single-ion anisotropy and makes VI₃ a candidate 2D Ising ferromagnet; Monte Carlo on this model puts a monolayer near 70 K, higher under tensile strain, which stabilises that state further. Band calculations without correlations make VI₃ a metal, while experiment finds a gap of 0.6–0.67 eV, so correlations have to be included.

For experimentalists · your lens

Torque and angle-dependent magnetisation put the easy axis about 40° from c; heat capacity and diffraction show the transitions near 79 and at 32 K; magneto-optical Kerr imaging shows the domains. Reported structures disagree, so state the temperature and the structure assumed when giving results.

For engineers · your lens

A Curie temperature near 50 K rules out practical magnetic devices. What VI₃ offers is a hard, strongly anisotropic layered magnet with a small gap – a building block for studying coercivity and orbital moments in van der Waals heterostructures.

In the research tracks

Theory frontiers

Magnetic order in two dimensions

Recent news

The newest items tagged VI₃, from the news feed updated 22 Oct 2026.

Preprintnot yet peer reviewed 2 Jul 2026 arXiv

Magnetic ordering in VI3: a van der Waals material combining vastly different magnetic anisotropies

Among magnetic van der Waals materials, the vanadium trihalide family exhibits unique features. In particular, VI3 contains V atoms of two different types, as two energetically close electronic occupations can coexist in real samples. These types show strikingly different magnetic anisotropy, predicted to differ by…

TheoryVI₃

Preprintnot yet peer reviewed 5 Dec 2025 arXiv

Valence Modifications in Hygroscopic VI3 Degraded Crystals via Soft X-Ray Synchrotron Radiation

Among van der Waals crystals, transition metal trihalide VI3 has driven attention for its magnetic and orbital properties. However, its chemical instability under ambient conditions make its exploitation challenging for technological implementation. In this context, here we show how synchrotron radiation soft X-rays…

TheoryCrI₃ VI₃

All 2 items tagged VI₃ in the news feed · RSS feed for VI₃

Key references

VI₃ – a new layered ferromagnetic semiconductorKong et al. · Advanced Materials 31, 1808074 (2019)cited by 220doi:10.1002/adma.201808074
Ferromagnetic van der Waals crystal VI₃Tian et al. · Journal of the American Chemical Society 141, 5326 (2019)doi:10.1021/jacs.8b13584
Bulk properties of the van der Waals hard ferromagnet VI₃Son et al. · Physical Review B 99, 041402 (2019)doi:10.1103/PhysRevB.99.041402
Crystal structures and phase transitions of the van der Waals ferromagnet VI₃Doležal et al. · Physical Review Materials 3, 121401 (2019)doi:10.1103/PhysRevMaterials.3.121401
Crystal structure evolution in the van der Waals vanadium trihalidesKratochvílová et al. · Journal of Physics: Condensed Matter 34, 294007 (2022)doi:10.1088/1361-648X/ac6d38
Magnetic anisotropy in the van der Waals ferromagnet VI₃Koriki et al. · Physical Review B 103, 174401 (2021)doi:10.1103/PhysRevB.103.174401
VI₃: a two-dimensional Ising ferromagnetYang et al. · Physical Review B 101, 100402 (2020)doi:10.1103/PhysRevB.101.100402

Download these references as BibTeX or RIS for Zotero, EndNote or Mendeley.