Cr2TiC2-based double MXenes: novel 2D bipolar antiferromagnetic semiconductor with gate-controllable spin orientation toward antiferromagnetic spintronics.

Antiferromagnetic (AF) spin devices could be one of the representative components for applications of spintronics thanks to the numerous advantages such as resistance to magnetic field perturbation, stray field-free operation, and ultrahigh device operation speed. However, detecting and manipulating the spin of AF materials is still a major challenge due to the absence of a net magnetic moment and spin degeneracy in the band structure. Bipolar antiferromagnetic semiconductors are promising solutions to these problems. Herein, using density functional theory calculations, we present asymmetrical functionalized double MXenes (Cr2TiC2FCl) that behave as a novel bipolar antiferromagnetic semiconductor (BAFS) with vanishing magnetism, in which the valence band and conduction band around the Fermi level exhibit opposite spin directions. Remarkably, gate voltage can manipulate the spin orientation of the AF Cr2TiC2FCl and lead to a transition from BAFS to half-metal antiferromagnets (HMAF). Moreover, the mixed functionalized double MXenes with various F/Cl concentrations show the BAFS feature due to the different chemical environment for the Cr atom. Our results presented herein open a new strategy towards AF spintronics and the realization of the AF spin field effect transistor.