The College of Education for Pure Sciences in the Department of Physics discussed a doctoral thesis on (a theoretical study of the physical properties of monolayer materials (AgN, VBi, KN, and VTe) based on density functional theory)
The thesis presented by the researcher (Mustafa Muhammad Jawad) included that semimetallic binary compounds have very wonderful properties, because they have high Curie temperatures and have a spin polarization equal to 100% at the Fermi level. Because of these properties, they are useful in spin electron devices. In this thesis, we studied the electronic, structural, magnetic and optical properties of several binary compounds in the bulk state as well as the monolayer state using first principles of the full-potential linear plane wave method based on density functional theory.
The compound VTe was studied; The half-metal characteristic appeared in the bulk state at the equilibrium lattice constant Å 8.54, in addition to an energy gap of 1.19 eV in the downward twist channel. It maintains the semimetallic (HM) characteristic at the transition to the monolayer, with an energy gap of 0.36 eV at the equilibrium lattice constant Å 12.1. According to the Slater-Poulenc rule (Zt - 8), the value of the magnetic moment of the unit cell is µB3. We investigated how the electronic and magnetic properties of the monolayer are affected by biaxial stress and electric field. The amount of energy gap in the twist-down channel changes under biaxial stress, in particular, it decreases under tensile stress and increases under compressive stress, and the magnetic moment values remain unchanged. Hence, preserving the (HM) property. Electric fields have a significant effect on the monolayer and clear consequences on the magnitude of the energy gap. However, at all values of the applied electric field, this compound retains its semimetallic character. Furthermore, the optical properties of spin-down channels have semiconductor properties and can be used in optoelectronic devices. The results show that this compound can be used in spintronic device applications.
The compound VBi was also studied; The half-metal characteristic appeared in the bulk state at the equilibrium lattice constant Å 6.32, in addition to an energy gap of 0.65 eV in the downward spin channel. It maintains the semimetallic (HM) characteristic at the transition to the monolayer, with an energy gap of 0.59 eV at the equilibrium lattice constant of 8.2 Å. According to the Slater-Poulenc rule (Zt - 8), the value of the magnetic moment of the unit cell is µB2. To analyze the electronic properties of a material, the band structure of the material and the total and partial densities of states must be calculated, which show that the material is semimetallic. Calculations are performed on the monolayer by applying an electric field and biaxial stress in order to determine its frequency-dependent electronic, magnetic and optical properties. This compound will lose its semimetallic property when the value of the applied electric field V/nm reaches 0.6.