Intrinsic 2D-XY ferromagnetism in a van der Waals monolayer

• Published in: Science (American Association for the Advancement of Science) Vol. 374; no. 6567; pp. 616 - 620
• Main Authors: Bedoya-Pinto, Amilcar, Ji, Jing-Rong, Pandeya, Avanindra K, Gargiani, Pierluigi, Valvidares, Manuel, Sessi, Paolo, Taylor, James M, Radu, Florin, Chang, Kai, Parkin, Stuart S P
• Format: Journal Article
• Language: English
• Published: United States The American Association for the Advancement of Science 29-10-2021
• Subjects: Anisotropy; Antiferromagnetism; Chromium; Circular dichroism; Dichroism; Epitaxial growth; Ferromagnetism; Fluids; Graphene; Iodides; Ising model; Magnetic anisotropy; Magnetic properties; Magnetism; Magnets; Molecular beam epitaxy; Monolayers; Phase transitions; Scaling; Silicon carbide; Superfluidity; Two dimensional materials
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.abd5146

The physics and universality scaling of phase transitions in low-dimensional systems has historically been a topic of great interest. Recently, two-dimensional (2D) materials exhibiting intriguing long-range magnetic order have been in the spotlight. Although an out-of-plane anisotropy has been shown to stabilize 2D magnetic order, the demonstration of a 2D magnet with in-plane rotational symmetry has remained elusive. We constructed a nearly ideal easy-plane system, a single CrCl
monolayer on graphene/6H-SiC(0001), and observed robust ferromagnetic ordering with critical scaling characteristic of a 2D-XY system. These observations indicate the realization of a finite-size Berezinskii-Kosterlitz-Thouless phase transition in a large-area, quasi–free-standing van der Waals monolayer magnet with an XY universality class. This offers a material platform to host 2D superfluid spin transport and topological magnetic textures.