Emerging 2D magnetic states in a graphene-based monolayer of EuC6

Recent discoveries of intrinsic two-dimensional (2D) magnets open up vast opportunities to address fundamental problems in condensed matter physics, giving rise to applications from ultra-compact spintronics to quantum computing. The ever-growing material landscape of 2D magnets lacks, however, carbon-based systems, prominent in other areas of 2D research. Magnetization measurements of the Eu/graphene compound—a monolayer of the EuC6 stoichiometry—reveal the emergence of 2D ferromagnetism but detailed studies of competing magnetic states are still missing. Here, we employ element-selective X-ray absorption spectroscopy (XAS) and magnetic circular dichroism (XMCD) to establish the magnetic structure of monolayer EuC6. The system exhibits the anomalous Hall effect, negative magnetoresistance, and magnetization consistent with a ferromagnetic state but the saturation magnetic moment (about 2.5 µB/Eu) is way too low for the half-filled f-shells of Eu2+ ions. Combined XAS/XMCD studies at the Eu L3 absorption edge probe the EuC6 magnetism in high fields and reveal the nature of the missing magnetic moments. The results are set against XMCD studies in Eu/silicene and Eu/germanene to establish monolayer EuC6 as a prominent member of the family of Eu-based 2D magnets combining the celebrated graphene properties with a strong magnetism of europium.