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Transition-metal trihalides

MX₃ (M = Cr, V, Ti, Fe; X = Cl, Br, I)

Also called CrI₃, CrBr₃, CrCl₃, VI₃, TiCl₃, FeCl₃, chromium trihalides

van der Waals crystal magnet

The first magnet made of a single layer of a van der Waals crystal. In 2017 a monolayer of chromium triiodide was shown to be a ferromagnet: without a preferred spin direction this is forbidden in two dimensions, and CrI3 escapes because its spins prefer to point out of the plane. Two stacked layers align opposite to each other, and that layered magnetic order can be flipped with a voltage, opening the way to magnetic devices built from 2D stacks. The same honeycomb layer with other metals behaves very differently: VI3 is a ferromagnetic semiconductor, the titanium ions in TiCl3 pair up and stop being magnetic below 217 K, and FeCl3 is best known as the compound slipped between graphene layers to make them conduct almost like a metal.

Key properties

  • Monolayer CrI3 is an Ising-like ferromagnet with a Curie temperature of ~45 K (bulk ~61 K)
  • Bilayer CrI3 couples antiferromagnetically between layers, unlike bulk – a consequence of different stacking in thin flakes
  • Interlayer magnetic order in bilayers can be switched electrically
  • Very large tunnelling magnetoresistance in graphene/CrI3/graphene spin-filter junctions at low temperature
  • Monolayer CrCl3 has in-plane (XY-type) anisotropy, a test case for Berezinskii–Kosterlitz–Thouless physics
  • The halides mix: CrBrxCl3−x and CrBrxI3−x form across the whole composition range, with lattice parameters close to Vegard’s law, near-infrared photoluminescence that shifts with composition, and a change of stacking in the chloride–bromide series at x ≈ 1.8
  • VI3 is a ferromagnetic semiconductor with a Curie temperature of ~50 K
  • TiCl3 (d1) forms Ti–Ti pairs 3.43 Å apart at a first-order transition at 217 K, where its magnetic susceptibility drops
  • FeCl3 intercalated into few-layer graphene gives films that are both highly conductive and transparent

How it is made

  • Vapour-transport growth of bulk crystals from chromium and iodine
  • Short chemical vapour transport straight onto yttria-stabilised zirconia, planned by thermodynamic simulation: CrCl3, CrBr3 and CrI3 sheets at most 25 nm thick grow in one step, and ultrasonic delamination takes CrCl3 down to monolayers
  • Mixed-halide nanoplatelets a few nanometres high by the same route; the halide ratio barely shifts during transport, so the starting powder sets the composition
  • α-TiCl3 microsheets about 4 µm thick on zirconia substrates, by vapour transport with GaCl3 added as a transport aid
  • Mechanical exfoliation and hBN encapsulation inside a glovebox
  • MBE growth of monolayer CrBr3 and CrCl3 on graphene or metal substrates
  • Vapour-phase intercalation of FeCl3 into few-layer graphene

Uses, and how close they are

  • Spin-filter tunnel junctions and magnetic memory conceptslab
  • Magnetic proximity effects in heterostructures (e.g. valley splitting in WSe2)lab
  • Transparent conductors from FeCl3-intercalated few-layer graphenelab
  • Ziegler–Natta catalysis: α-TiCl3 is an established catalyst for polyethylene, and vapour-grown microsheets were 16% more active than bulk, up to 24% after delaminationlab

Readiness runs lab → prototype → pilot → deployed.

Open problems

  1. Why does stacking in thin CrI3 differ from bulk, and can stacking-controlled magnetism be engineered deliberately?
  2. Can the Curie temperature be raised towards room temperature by strain, doping or pressure?
  3. Are there topological magnons, and what opens the gap at the magnon Dirac points?
  4. Does the Ti–Ti pairing of bulk TiCl3 survive in thin flakes, and what does a single layer do instead?
  5. What ordering in mixed-halide CrX3 crystals produces the extra X-ray reflections that neither parent structure explains?

Going deeper

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

For theoreticians · your lens

Magnetic anisotropy, originating in the halide spin–orbit coupling, is what lets a monolayer order despite the Mermin–Wagner theorem, so SOC is essential. Minimal spin models need Heisenberg exchange plus single-ion and anisotropic (including Kitaev-type) terms. Interlayer exchange changes sign with stacking, which DFT captures only with careful dispersion corrections and U; Curie temperatures require Monte Carlo or renormalised spin-wave theory rather than mean field. Changing the metal changes the physics: d3 chromium gives robust spin-3/2 moments, d2 vanadium in VI3 adds orbital degrees of freedom that DFT+U handles poorly, and d1 titanium in TiCl3 dimerises instead of ordering magnetically.

For experimentalists · your lens

Probe magnetism optically with magneto-optical Kerr effect or reflective magnetic circular dichroism in a cryostat; thickness-dependent hysteresis loops distinguish ferromagnetic monolayers, antiferromagnetic bilayers and layered antiferromagnetic few-layers. Raman shows magnon and magnetic-order-dependent phonon features. Keep samples inert and dark until encapsulated. The 217 K transition of TiCl3 shows up as a step with thermal hysteresis in the magnetic susceptibility.

For engineers · your lens

Low Curie temperatures and severe air sensitivity rule out magnetic applications today. Their importance is as proof that 2D magnetic heterostructures work; the engineering path runs through higher-Tc, air-stable van der Waals magnets. The nearest practical uses in the family are elsewhere: FeCl3 inside few-layer graphene as a transparent conductor, and α-TiCl3 as a Ziegler–Natta polymerisation catalyst, where thinner sheets have proved more active.

In the research tracks

Theory frontiers

Growth methods

Recent news

The newest items tagged CrI3, VI3, TiCl3, from the news feed updated 5 Oct 2026.

Preprintnot yet peer reviewed arXiv

Binary magnetism and directional magnon transport in alkali-doped CrI3

The recent realization of two-dimensional (2D) magnets, with CrI3 as a pioneering example, has opened new avenues in the fields of 2D materials and magnetism. This breakthrough has been followed by extensive efforts to manipulate and exploit their magnetic properties. In this work, we investigate the adsorption of…

ExperimentCrI₃, VI₃, TiCl₃
Preprintnot yet peer reviewed arXiv

Engineering nonlinear spin-orbit torque driven by intra-band transport in MoSe2/CrI3 and WSe2/CrI3 van der Waals heterostructures

The role of nonlinear carrier dynamics in current-driven spin phenomena remains poorly understood in van der Waals magnetic heterostructures. Here, we investigate the spin polarization and the resulting spin-orbit torque (SOT) in transition-metal dichalcogenide/chromium iodide (TMDC/CrI3) heterostructures, focusing on…

TheoryExperimentMoSe₂WSe₂CrI₃, VI₃, TiCl₃

All 28 items tagged CrI₃, VI₃, TiCl₃ in the news feed  ·  RSS feed for CrI₃, VI₃, TiCl₃

Key references

  1. Layer-dependent ferromagnetism in a van der Waals crystal down to the monolayer limitHuang et al. · Nature 546, 270 (2017)cited by 5,987doi:10.1038/nature22391
  2. Electrical control of 2D magnetism in bilayer CrI3Huang et al. · Nature Nanotechnology 13, 544 (2018)cited by 1,373doi:10.1038/s41565-018-0121-3
  3. Intrinsic 2D-XY ferromagnetism in a van der Waals monolayerBedoya-Pinto et al. · Science 374, 616 (2021)cited by 250doi:10.1126/science.abd5146
  4. VI3 – a new layered ferromagnetic semiconductorKong et al. · Advanced Materials 31, 1808074 (2019)cited by 210doi:10.1002/adma.201808074
  5. Magnetic study of a phase transition at 217 K in α-TiCl3Tsutsumi et al. · Journal of Magnetism and Magnetic Materials 90–91, 181 (1990)cited by 3doi:10.1016/S0304-8853(10)80063-0
  6. Novel highly conductive and transparent graphene-based conductorsKhrapach et al. · Advanced Materials 24, 2844 (2012)cited by 336doi:10.1002/adma.201200489
  7. Chromium trihalides CrX3 (X = Cl, Br, I): direct deposition of micro- and nanosheets on substrates by chemical vapor transportGrönke et al. · Advanced Materials Interfaces 6, 1901410 (2019)cited by 60doi:10.1002/admi.201901410
  8. Layered α-TiCl3: microsheets on YSZ substrates for ethylene polymerization with enhanced activityGrönke et al. · Chemistry of Materials 31, 5305 (2019)cited by 9doi:10.1021/acs.chemmater.9b01818
  9. Controlled nanoplatelet deposition of 2D chromium trihalide solid solutionsFroeschke et al. · Chemistry of Materials 35, 4136 (2023)cited by 5doi:10.1021/acs.chemmater.2c03785
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