Layer dependent magnetism and topology in monolayer and bilayers ReX 3 (X = Br, I)

Abstract

The realization of robust intrinsic ferromagnetism in two-dimensional materials with the possibility to support topologically non-trivial states has provided the fertile ground for novel physics and next-generation spintronics and quantum computing applications. In this contribution, we investigated the formation of topological states and magnetism in monolayer and bilayer systems of ReX 3 (X = Br, I), with PBE, ACBN0 (self-consistent Hubbard-U), excluding/including van der Waals (vdW) corrections and/or spin–orbit coupling. Bulk ReX 3 (X = Br, I) is predicted to crystallize in space group (#148), similar to CrI3, with monolayer exfoliation energies that are comparable or less than that of graphite. The topological character of the monolayer and bilayer systems of ReX 3 (X = Br, I) is derived from anomalous Hall conductivity computations. Topologically non-trivial states in ReX 3 (X = Br, I) are absent in the Hubbard-U computations if vdW interactions are included, a prediction that is attributed to the large Hubbard-U difference between the chemical constituents, ΔU ∼ 1.5–1.6 eV, and a significant ∼2.0%–3.6% compressive in-plane strain introduced by vdW interactions. In contrast to the fragile and likely absent topological states in ReX 3 (X = Br, I), magnetic properties are robust and independent of the level of theory: ferromagnetic monolayers are coupled antiferromagnetically to bilayers, with an energy separation between ferromagnetic and antiferromagnetic bilayer spin configurations that could be as low as 0.02 meV/Re (f = 4.8 GHz), well within the microwave range. This suggests that layer dependent magnetism in ReX 3 (X = Br, I) may support a microwave controllable magnetic qubit, consisting of a superposition of antiferromagnetic and ferromagnetic bilayer states.