A candidate exchange-biased vdW heterostructure based on Cr2NO2 and Cr2CF2 MXenes

Abstract

We investigated the van der Waals heterostructure Cr₂NO₂/Cr₂CF₂ by spin-polarized first-principles calculations. The aim is to create two-dimensional ferromagnetic/antiferromagnetic heterostructures where the exchange bias effect can occur. Cr₂NO₂ MXene is a half-metal ferromagnetic material, while Cr₂CF₂ MXene is an antiferromagnetic semiconductor. The lattice mismatch of both MXenes is ∼4%, good enough to construct the heterostructure. Three different stackings were considered in the heterostructure: H3, T4, and Top. Also, three different cell parameters are considered: larger lattice constant a(Cr₂CF₂), shorter lattice constant a(Cr₂NO₂), and both relaxed. In all cases, T4 staking is the most favorable interaction configuration. Non-covalent interactions show that van der Waals forces dominate in the heterostructure. Also, the average electrostatic potential along the z-axis explains the stability in the T4 stacking. Antiferromagnetic coupling is the most stable when fixing a(Cr₂CF₂) as the heterostructure lattice parameter, while for the short lattice constant, a(Cr₂NO₂), the magnetic coupling becomes Ferromagnetic. Band diagrams evidence that both MXenes preserve their electronic properties after the interaction, so the antiferromagnetic alignment is intrinsic in the heterostructure for the larger lattice constant. Our theoretical findings open the door to consider the versatile MXenes as promising candidates for the new generation of information storage nanodevices.