Competing magnetic states in silicene and germanene 2D ferromagnets

Abstract

Two-dimension (2D) magnets have recently developed into a class of stoichiometric materials with prospective applications in ultra-compact spintronics and quantum computing. Their functionality is particularly rich when different magnetic orders are competing in the same material. Metalloxenes REX2 (RE = Eu, Gd; X = Si, Ge), silicene or germanene — heavy counterparts of graphene — coupled with a layer of rare-earth metals, evolve from three-dimension (3D) antiferromagnets in multilayer structures to 2D ferromagnets in a few monolayers. This evolution, however, does not lead to fully saturated 2D ferromagnetism, pointing at a possibility of coexisting/competing magnetic states. Here, REX2 magnetism is explored with element-selective X-ray magnetic circular dichroism (XMCD). The measurements are carried out for GdSi2, EuSi2, GdGe2, and EuGe2 of different thicknesses down to 1 monolayer employing K absorption edges of Si and Ge as well as M and L edges of the rare-earths. They access the magnetic state in REX2 and determine the seat of magnetism, orbital, and spin contributions to the magnetic moment. High-field measurements probe remnants of the bulk antiferromagnetism in 2D REX2. The results provide a new platform for studies of complex magnetic structures in 2D materials.