Effects of transition metals and earth alkaline metals in the ionic honeycomb monolayer sodium bromide towards spintronic applications

Abstract

Chemical modification through doping is an efficient way to functionalize two-dimensional (2D) materials. Using first-principles calculations, the electronic and magnetic properties of a sodium bromide (NaBr) monolayer doped with transition metals (V, Cr, Mn, and Fe) and earth alkaline metals (Be, Mg, Ca, and Sr) are investigated. The NaBr monolayer is dynamically and thermally stable, exhibiting insulator behavior with an indirect gap of 4.52 eV. Its ionic character is also confirmed by the charge distribution and electron localization function. Our calculations show that a single Na vacancy magnetizes significantly the monolayer, where the magnetic properties are produced mainly by Br atoms closest to the defect site. High magnetization of this 2D material can be also achieved by doping with transition metals, which is reflected in large total magnetic moments between 3.66 and 5.00 μ_B. Herein, the half-metallicity is induced by doping with V and Fe atoms, while Cr and Mn impurities lead to the emergence of the magnetic semiconductor nature. The monolayer is metallized by doping with Be atoms, preserving its non magnetic nature. In contrast, significant magnetism with total magnetic moment of 1.00 μ_B is obtained by doping with Mg, Ca, and Sr atoms. In these cases, the magnetic semiconductor nature also emerges because of new middle-gap electronic states. In all cases, impurities act as charge losers, transferring a certain charge quantity to the host monolayer. Moreover, dopant atoms play a key role in originating the magnetism and determining the electronic behavior of the doped systems. The results presented herein introduce prospects of the doped NaBr monolayer to be applied in spintronic nano devices.