Designed two dimensional transition metal borides (TM2B12): Robust ferromagnetic half metal and antiferromagnetic semiconductor

Abstract

Two dimensional transition metal borides have been attracting broad interest due to its rich electronic and magnetic properties. Here, using first-principles calculations, we predict two transition metal boride monolayers, Cr2B12 and Mn2B12, composed of B12 icosahedra and transition metal atoms. It is found that both structures are thermodynamically stable with large cohesive energies and small formation energies. The Cr2B12 monolayer is a ferromagnetic (FM) quasi-half metal, and the Mn2B12 monolayer is an antiferromagnetic (AFM) semiconductor with a bandgap of 0.41 eV. The critical temperature is found to be 145 and 135 K for the Cr2B12 monolayer and the Mn2B12 monolayer, respectively. Moreover, the electronic and magnetic properties of both systems can be tuned by applying external strains. Upon applying biaxial tensile/compressive strain, the (half metallic) bandgap of both systems increases/decreases, and a quasi-half metal to half metal transition is found for the Cr2B12 monolayer under 5% tensile and 4% compressive strain. Furthermore, the critical temperatures of both systems are found to increase with compressive strain and decrease with tensile strain, which reaches 165 and 510 K for the Cr2B12 monolayer and the Mn2B12 monolayer under 5% compressive strain, respectively. The results provide a strategy for designing 2D transition metal borides with potential applications in electronic and spintronic devices.

Two-Dimensional Transition Metal Boride TMB12 (TM = V, Cr, Mn, and Fe) Monolayers: Robust Antiferromagnetic Semiconductors with Large Magnetic Anisotropy

“…The T N s can be obtained by locating the peak of the susceptibility, which are 20 K, 35 K, 90 K, and 135 K for the VB 12 monolayer, the CrB 12 monolayer, the MnB 12 monolayer, and the FeB 12 monolayer, respectively. Such magnetic transition temperatures are comparable with the reported Cr 2 B 12 (145 K) and Mn 2 B 12 (135 K) monolayers [51]. On the other hand, we should state that the magnetic transition temperatures of the predicted systems are much lower than room temperature, which blocks their applications in spintronic devices.…”

“…The energy cutoff for the plane-wave basis set was set to 500 eV, and the vacuum spaces were larger than 15 Å to eliminate the physical interactions caused by periodic boundary conditions. For transition metal atoms V, Cr, Mn, and Fe, a GGA + U method with U eff = 4.0 eV was adopted to treat the Coulomb and exchange interactions of the 3d-electron according to previous studies [38,51,64,65]. The k mesh was set as 9 × 9 × 1, 5 × 9 × 1, and 5 × 5 × 1 for FM, AFM-1, and AFM-2 geometry optimization, and a denser k-mesh of 27 × 27 × 1, 15 × 27 × 1, and 15 × 15 × 1 was adopted for electronic structure calculations.…”

“…As the valence states of the B atom are unsaturated, it can easily hybridize with exotic atoms and display distinct electronic properties. Currently, a number of 2D TM borides with rich stoichiometries and geometric configurations have been predicted in theory and synthesized in experiments, such as TMB x (x = 1-6, 8, 9, 12) [37][38][39][40][41][42][43][44][45][46][47], TM n B n (n = 1, 2) [37,38,48], TM n B m (n = 2, m = 3, 6, 12) [49][50][51], etc., and robust magnetic properties have been found in these TM borides. For example, Ozdemir et al found that an Fe 2 B 2 monolayer with rectangular lattice and Fe atoms in different atomic planes has a stable columnar AFM ground state, which can change to an FM order with double hysteresis behavior [48].…”