First-Principles Study Of Electronic Structure And Magnetic Properties Of Orthorhombic CrGa₂Sb₂ And MnGa₂Sb₂

In recent years, studies on the semiconductor spintronic are emphasized, and the results indicate that the diluted magnetic semiconductors are the candidates for spintronic applications due to which can be used to manage and store information by means of the electronic charge and spin. The ferromagnetic transition temperature of many DMS is low, and the Curie temperature is under room temperature, because the solubility of magnetic ion into the DMS is very small. Later, the researchers found that the intermetallics have high spin polarization and Curie temperature above room. Such as Cr Ga2Sb2 and Mn Ga2Sb2 synthesized on experiment, in which the solubility of magnetic Cr/Mn ions is high, and the Curie temperature is above room temperature. The experimental results show that Mn Ga2Sb2 is a metal, while Cr Ga2Sb2 has the semiconductor property. The theoretical results of Mn Ga2Sb2 is agree with the experiment results, but the theoretical results of Cr Ga2Sb2 show it is a metal, which is not agree with the experiment results. So in this thesis, the electronic structure and magnetic properties on the intermetallics Cr Ga2Sb2 and Mn Ga2Sb2 with the linear chains of transition-metal are investigated comprehensively, using the full-potential linear augmented plane wave + local orbit(FPLAPW+lo) based on the density functional theory(DFT).We use four different exchange correlation potentials: the local density approximation(LDA), the generalized gradient approximation(GGA), GGA+U, and the Tran-Blaha modified Johnson functional(m BJ) to calculate Cr Ga2Sb2 and Mn Ga2Sb2. The electronic structure calculations from four exchange correlation potentials show that Cr Ga2Sb2 is a pseudogap(negative gap) material with very small density of states(DOS) at the Fermi level, while Mn Ga2Sb2 has notably higher DOS at the Fermi level compared to Cr Ga2Sb2, exhibiting stronger metallic conductivity, although the m BJ potential obtains lower DOS at the Fermi level than LDA and GGA for both Cr Ga2Sb2 and Mn Ga2Sb2. The GGA+U method with a small value(1e V) of the on-site Coulomb interaction parameter U obtains lower DOS at the Fermi level compared to the large value of U. In agreement with the measurement data, the total energy calculations reveal that both Cr Ga2Sb2 and Mn Ga2Sb2 have a stable ferromagnetic ground state with lower energies relative to antiferromagnetic state. Based on the Heisenberg model, the magnetic exchange constants between the nearest-neighbor Cr-Cr and Mn-Mn along transition-metal linear chains are calculated to be 48.6 me V and 27.5 me V for Cr Ga2Sb2 and Mn Ga2Sb2, respectively. By the mean-field approximation method, we calculated the Cure temperature of two to be above room-temperature.