First-principles study of electronic structure , magnetic and optical properties of Ti, V, Co and Ni doped two-dimensional CrSi<sub>2</sub> materials

Abstract

<sec>Two-dimensional materials have shown excellent optical, mechanical, thermal or magnetic properties, and have promising applications in the high performance electronic, optical, spintronic devices and energy transfer, energy storage, etc. Monolayer transition metal silicide CrSi<sub>2</sub> has shown ferromagnetism and metal properties in previous studies, and it is expected to become a new two-dimensional material. The Ti, V, Co, Ni doped two-dimensional CrSi<sub>2</sub> are studied with different doping concentrations by using the first-principal pseudopotential plane wave method based on density functional theory, and electronic structure, magnetic and optical properties are calculated and analyzed. The results show that the density of states in the two-dimensional CrSi<sub>2</sub> system is asymmetric, and the crystal cells have obvious ferromagnetism with a magnetic moment of 3.55 <i>μ</i>B. Two-dimensional CrSi<sub>2</sub> has strong absorptivity and reflectivity in the far infrared and ultraviolet range, showing excellent optical properties.</sec><sec>The electronic structures and magnetic properties of Ti, V, Co or Ni doped CrSi<sub>2</sub> with different concentrations are calculated and analyzed, and the results show that the magnetic moment of the two-dimensional CrSi<sub>2</sub> varies after doping different elements at a doping concentration of 3.70 at%. After doping Ti, the magnetic moment of the system changes to 0 <i>μ</i>B at a doping concentration of 3.70 at%, showing that it is an indirect semiconductor. After doping V, the magnetic moment becomes smaller at a doping concentration of 3.70 at%, and the system has two degrees of freedom: electron charge and spin, showing the properties of diluted magnetic semiconductors. After doping Ni, the band gap <i>E</i><sub>g</sub>=0.09 eV appears in the spin-up band of the system at a doping concentration of 3.70 at%, while the spin-down band is metallic, and the system shows semi-metallic properties. The magnetic moment changes to 3.71 <i>μ</i>B after doping Ti at a doping concentration of 7.41 at%. After doping Co and Ni, the magnetic moment of the system becomes smaller at the doping concentration of 7.41 at%, and the spin-down 3<i>d</i> orbital electrons of ferromagnetic elements take the dominant position. After doping Ni, the magnetic moment becomes 0.37 <i>μ</i>B at the doping concentration of 7.41 at%. After doping Ti, the magnetic moment becomes 2.79 <i>μ</i>B at a doping concentration of 33.3 at at%, after doping V, the magnetic moment becomes 2.27 <i>μ</i>B, and the degree of spin becomes weaker at a doping concentration of 11.1 at%. After doping Co, the magnetic moment becomes 1.81 <i>μ</i>B at the doping concentration of 11.1 at%. The magnetic moment becomes 1.5 <i>μ</i>B after doping Ni at the doping concentration of 11.1 at%, which proves that the spin-up <i>d</i> orbital has less electronic contribution to the magnetic moment. The energy band range of each system is enlarged, and the interaction between atoms is enlarged, and the energy level splitting energy is enlarged at the doping concentration of 11.1 at%, which indicates that the effective mass of the system becomes smaller, the mobility of carriers turns stronger, and the metallization of materials grows stronger.</sec><sec>The optical properties of Ti, V, Co or Ni doped CrSi<sub>2</sub> with different concentrations are calculated and analyzed, and the results show that the two-dimensional CrSi<sub>2</sub> after being doped has good optical properties. For most of systems, their optical properties are improved and blue-shifted at the doping concentrations of 3.70 at% and 7.41 at%, but the absorption peak is red-shifted at the doping concentration of 11.1 at%. By studying the properties of doped two-dimensional CrSi<sub>2</sub>, it is found that the two-dimensional CrSi<sub>2</sub> has excellent electronic structure and optical properties, and the electronic structure, magnetic and optical properties of the two-dimensional CrSi<sub>2</sub> can be effectively changed by doping. Two-dimensional CrSi<sub>2</sub> is expected to be a promising material for preparing new high reliability and high stability spintronic devices, and the present research provides an effective theoretical basis for developing the two-dimensional CrSi<sub>2</sub> based devices.</sec>