Prediction of 2D ferromagnetism and monovalent europium ions in the EuBr/graphene heterojunctions

TL;DR

This paper predicts that EuBr/graphene heterojunctions are 2D ferromagnetic metals with unique Eu ions, stable cation-π interactions, and tunable magnetic properties, promising for advanced electronic and spintronic applications.

Contribution

It introduces a novel 2D EuBr/graphene heterojunction with predicted ferromagnetism, metallicity, and stable Eu ions, expanding the potential for 2D magnetic materials.

Findings

Heterojunctions exhibit metallicity and strong ferromagnetism (~7.0 μB per Eu)

Stable cation-π interactions explain heterojunction stability

Curie temperature estimated at about 7 K, tunable by strain and doping

Abstract

Europium, one of the rare earth elements, exhibits +2 and +3 valence states and has been widely used for magnetic modification of materials. Based on density functional theory calculations, we predict the 2D EuBr/graphene heterojunctions to exhibit metallicity, huge intrinsic-ferromagnetism nearly 7.0 {\mu}B per Eu and the special monovalent Eu ions. Electron localization function (ELF), difference charge densities and Bader charge analyses demonstrate that there are cation-{\pi} interactions between the EuBr films and graphene, which explains the stability of these unusual heterojunctions. Graphene works as substrate to enable the stability of EuBr monolayer crystals where EuBr plays an important role to yield ferromagnetism and enhance metallicity in the heterojunctions. Monte Carlo simulations are used to estimate a Curie temperature of about 7 K, which, together with magnetic configurations, can be further modulated by external strains and charge-carrier doping. In general, our theoretical work predicts the properties of the novel 2D ferromagnetic EuBr/graphene heterojunctions, suggests the possibility of combining the 2D intrinsic-ferromagnetic metal halide crystals and graphene, and opens up a new perspective in next-generation electronic, spintronic devices and high-performance sensors.