Ab-initio and Monte Carlo study of Fe-based two-dimensional magnets at borophene supported by Ag(111) surface

Two-dimensional (2D) magnetic crystals are ideal platforms for the employment of simple physical models in the exploration of magnetism in a 2D limit. Instead of examining 2D van der Waals materials, the focus of our study is on adatoms that carry intrinsic magnetic moments and are assembled into 2D arrays at a suitable surface. We applied density functional theory (DFT) to investigate Fe nanostructures formed on a borophene sheet deposited at Ag(111) surface and identified stable Fe-based 2D magnets formed either on top of the borophene or at the interface between the borophene and Ag(111) surface. The structures are composed of close-packed Fe wires, featuring ferromagnetism within the chain and the interchain antiferromagnetic coupling. Exchange- and single-ion anisotropy constants extracted from DFT calculations are used to describe these systems with the classical Ising and Heisenberg models. The corresponding Monte Carlo simulations revealed finite temperature magnetic ordering, with the estimates of critical temperatures of 105 and 30 K derived from the anisotropic Heisenberg model, for the Fe-based magnets grown above and under borophene, respectively.