The First-Princle Calculation Of Mn-based Perovskite Oxide

The Density Functional Theory has become most powerful tool to investigatge electronic structure and material characteristics in condensed matter physics and material physics, since it was established in 1960s and followed by its famous export equation---Kohn-Sham equation. The first-principle calculation, which is based on the Density Functional Theory, is playing important role in computational materials. In recent years, the superiority of the first-principle calculation is becoming more and more outstanding to explore and design novel material due to the application of the large and high-speed computer.Perovskite oxide is very important subjects in magnetic material, among of which double perovskite La2NiMn06 and La2CoMnO6(hereafter called LNMO and LCMO) are both kinds of ferromagnetic semiconductor with high Curie temperature (～270°),which has attracted much more attention in both theory and experiment. It is very interesting to investigate their special electronic structure and magnetic propertise using first-principle calculation. In this thesis, we focus on changes of property when Ba, Sr, Ca atoms are dopped instand of the A-site atom.The electronic structure and crystal structure of LNMO and LCMO are investigated carefully. In order to understand the effect of La-site dopping on crystal structure and magnetic property, we studied the electronic structure and magnetic properties of both LNMO and LCMO.Our results serve as a first quantitative theoretical prediction for future study, and the main work are listed as follows:1,The structural, electronic and magngetic properties of monoclinic P21/n double perovskite LNMO and LCMO were studied using first-principle desity functional calculations, and the internal bonding regularity and valence state are also analysed.We found LNMO and LCMO are both ferromagnetic insulator in P21/n monoclinic crystal strucuture. For LNMO, our calculations show that the GGA calculation results are coincide with the experiment. The magnetic moment of LNMO are 5μB, and 1.47μBand 2.65μB for Ni and Mn, respectively. But for LCMO, the LDA+U calculation results are coincide with the experiment. The magnetic moment of LCMO are 6μB, and 2.63μB and 3.16μB for Co and Mn, respectively. Above all, the valence state of Ni, Co and Mn are+2 and+4, respectively.2, Discussing the different degree effects of doping La on its structure and magnetic properties, and explaining the reseaon for the change of every kinds of atoms' magnetic moment when dopping La-site by electronic structure and band structure.25%,50% and 75% La replaced by Sr results in half-metal ferromagnetism in LNMO. In contrast, only 25% Sr dopping in LCMO behave half-metal ferromagnetism. We analyzed how the electronic structure and crystal structure changed with Sr dopped concentration in details.Our results reveal that the M-O-Mn angle (M is Co or Ni) of the two octahedrons(NiO6/CoO6 and MnO6)is increasing with Sr concentration, The related change trendency of chemical bonding and magnetic are consistent with famous GK rules.