Magnetism in Cleavable Transition Metal Halides

There is great interest in identifying cleavable magnetic materials to complement the variety of optical and electronic monolayer components currently available for van der Waals heterostructures. The layered compound CrI₃ was recently proposed as a promising candidate, and subsequently demonstrated as a monolayer ferromagnet with interesting layer-number dependent properties, and incorporated into van der Waals heterostructures with other 2D materials. These developments have brought increased attention to transition metal halide materials for the study of 2D physics and functional heterostructures. This large family of layered materials displays a wide variety of magnetic phenomena, including strong frustration, spin-liquid behavior, ferromagnetism, antiferromagnetism, and multiferroicity. Recent developments with CrI₃ monolayers, and other related transition metal halides will be presented, including antiferromagnetic CrCl₃ and the 4d transition metal analog MoCl₃, in which magnetism only appears well above room temperature.