Intrinsic magnetism in two-dimensional Cr₂X₂Se (X = I, Br, Cl) monolayers

¹ Department of Physics, Huaiyin Institute of Technology - 1 Meicheng East Road, Huaian 223003, China
² School of Physics Science and Engineering, Tongji University - 1239 Siping Road, Shanghai 200092, China
³ Department of Physics, The Hong Kong University of Science and Technology - Clear Water Bay, Kowloon, Hong Kong, China
⁴ Department of Physics, Jiangsu Normal University - Xuzhou 221009, China

^(a) jsblgao@163.com (corresponding author)
^(b) shke@tongji.edu.cn
^(c) phxwang@ust.hk

Received: 10 August 2021
Accepted: 4 November 2021

Abstract

A novel family of two-dimensional Cr₂X₂Se (X = I, Br, Cl) monolayers with intrinsic magnetism has been predicted using first-principles calculations. The monolayer with the five atomic sublayers has two structures: structure I with ABCAB-type atomic sublayers and structure II with ABCBA-type atomic sublayers. It is found that the lowest energy states are ferromagnetic (FM) half metal for the structure I, and antiferromagnetic (AFM) semiconductor for the structure II, respectively. Phonon spectrum calculations and molecular dynamics simulations show that these lowest energy magnetic states are stable. Monte Carlo simulations based on the Ising model show that the Curie temperatures are about 94, 156 and 93 K for Cr₂I₂Se, Cr₂Br₂Se and Cr₂Cl₂Se monolayers in the structure I, respectively, which are above 77 K of the liquid-nitrogen transition temperature. The large magnetocrystalline anisotropy energies of about 1879, 68, 28 μeV per Cr atom for Cr₂X₂Se (X = I, Br, Cl) monolayers in the structure I show their importance in magnetic memory and storage. The magnetization direction is out of plane in Cr₂I₂Se and Cr₂Br₂Se, but is in plane in Cr₂Cl₂Se. Our study implies a new route in 2D electronics and spintronics.