Voltage-gated spin-filtering properties and global minimum of planar MnB6, and half-metallicity and room-temperature ferromagnetism of its oxide sheet

Abstract

In view of the fabrication of transition metal (TM)-centered boron wheels and two-dimensional (2D) borophene, we predict a stable MnB₆ planar structure by means of density functional theory computations and global minimum structural search using efficient evolutionary algorithm. This 2D boron structure consists of a borophene-like plane and TM atoms with the P6/mmm space group. As revealed by moderate formation and cohesive energies, positive phonon modes, high melting temperature, and remarkable mechanical properties, it holds superior structural stability that must be experimentally realized. The band gap of 0.7 eV for spin-down electrons is located within the forbidden region of the 2.2 eV band gap for spin-up electrons, thus enabling the manipulation of spins by controlling the bias voltage. In addition, tensile strain can help obtain room-temperature ferromagnetism in this material. Furthermore, its Young's modulus is greatly enhanced compared with that of the experimentally fabricated borophene, showing in-plane stiffness similar to graphene. Its oxide sheet MnB₆O₂ also has good stability. Its distinct half-metallic and room-temperature ferromagnetic properties render it an attractive material for spintronics. The present work is the first report of the sandwich-like global minimum of planar TM-boron materials, opening the door for tailoring unique properties by manipulating TM atoms.