Layer-dependent ferromagnetism in a van der Waals crystal down to the monolayer limit

Title	Layer-dependent ferromagnetism in a van der Waals crystal down to the monolayer limit
Authors	Bevin Huang, Genevieve Clark, Efrén Navarro-Moratalla, Dahlia R. Klein, Ran Cheng, Kyle L. Seyler, Ding Zhong, Emma Schmidgall, Michael A. McGuire, David H. Cobden, Wang Yao, Di Xiao, Pablo Jarillo-Herrero, Xiaodong Xu
Magazine	Nature
Date	06/07/2017
DOI	10.1038/nature22391
Introduction	The emergence of graphene has led to a significant expansion in the field of two-dimensional materials, which exhibit diverse electronic properties. This group now encompasses semiconductors with spin–valley coupling, Ising superconductors adjustable into a quantum metal state, potential Mott insulators with modifiable charge-density waves, and topological semimetals featuring edge transport. Despite these advancements, a two-dimensional crystal possessing intrinsic magnetism had remained elusive, though such a material holds promise for applications in sensing and data storage. Theoretical frameworks, specifically the Mermin–Wagner theorem, generally preclude magnetic order in the two-dimensional isotropic Heisenberg model at finite temperatures. Nevertheless, magnetic anisotropy can bypass this limitation, facilitating the manifestation of two-dimensional Ising ferromagnetism. In this work, magneto-optical Kerr effect microscopy establishes that monolayer chromium triiodide (CrI3) functions as an Ising ferromagnet with an out-of-plane spin alignment. Its Curie temperature of 45 Kelvin is only marginally below that of the bulk crystal (61 Kelvin), indicating a weak interlayer coupling. Furthermore, our investigations reveal a layer-dependent magnetic phase, emphasising the thickness-sensitive physical characteristics inherent to van der Waals crystals. Notably, bilayer CrI3 exhibits reduced magnetisation alongside a metamagnetic effect, whereas trilayer CrI3 reinstates the interlayer ferromagnetism observed in its bulk form. This research opens avenues for investigating magnetism by leveraging the unique attributes of atomically thin materials, including electrical control for advanced magnetoelectronics and van der Waals engineering for generating novel interface phenomena.
Quote	Bevin Huang, Genevieve Clark and Efrén Navarro-Moratalla et al. Layer-dependent ferromagnetism in a van der Waals crystal down to the monolayer limit. Nature. 2017. Vol. 546(7657):270-273. DOI: 10.1038/nature22391
Element	Chromium (Cr) , Iodine (I)
Industry	Electronics , Research & Laboratory