Strain- and carrier-tunable magnetic properties of a two-dimensional intrinsically ferromagnetic semiconductor: CoBr2 monolayer

Abstract

The ${\mathrm{CoBr}}_{2}$ monolayer is predicted to be an intrinsically ferromagnetic (FM) semiconductor based on the first-principles calculations. The results of the magnetic anisotropy energy show that the ${\mathrm{CoBr}}_{2}$ monolayer has an easy magnetization plane and belongs to the family of two-dimensional $XY$ magnets. The exchange interactions and thus the magnetic properties can be effectively tuned by external strain and carrier doping. The biaxial tensile strain can induce FM-antiferromagnetic (AFM) phase transition in the ${\mathrm{CoBr}}_{2}$ monolayer, by which the Co-Br-Co bond angle is enlarged deviating far away from ${90}^{\ensuremath{\circ}}$. While the compressive strain stabilizes the FM state by reducing the nearest Co-Co distance and enhancing the $p\text{\ensuremath{-}}d$ hybridization between Co and Br atoms. The ${\mathrm{CoBr}}_{2}$ monolayer remains semiconducting for the whole range of strain investigated. For the carrier doping, however, the ${\mathrm{CoBr}}_{2}$ monolayer tends to be a half-metal for both hole and electron doping. Doping not only introduces itinerant carriers, but also enhances the $p\text{\ensuremath{-}}d$ hybridization between the Co and Br atoms, both of which enhance the FM coupling significantly. The tunability of the electronic and magnetic properties of ${\mathrm{CoBr}}_{2}$ monolayer makes it a promising candidate for future nanospintronic applications.