First-principles Calculations Study Of Brownmillerite Oxides

First-principles calculation method based on density functional theory has become one of the important methods for modern science to simulate the properties of materials.It has a wide range of roles in research fields such as physics and chemistry.First-principles calculation is to use modern computer technology to simulate various physical and chemical properties of materials,to deeply understand the phenomena and characteristics of materials at multiple scales from micro to macro,and to predict the structure and physical properties of materials,so as to achieve the purpose of designing new materials.Transition metal associated electronic materials exhibit abundant magnetic properties due to the coupling and competitive effects of the degrees of freedom such as spin,charge,orbit and lattice.The development of new spintronic devices urgently needs high quality magnetic carrier materials to bring revolutionary breakthroughs for the next generation of information storage and quantum computing technology.One of the spin channels of the magnetic semimetals is metallic and the other is insulator,which can generate 100%efficient polarization current,and is an important class of spintronics materials.Brownmillerite oxides is derived from the common ABO₃ perovskite oxide by vacancy substitution of one-sixth of the oxygen ions.In this paper,the physical properties of B-position atoms substituted by different transition metal atoms in ABO_2.5,a calcium ferrite oxide,were studied by first principles calculations.The properties of the material are controlled by changing the atomic ratio.The compounds Sr₂B_2-xB?_xO₅(x=0.5,1,1.5;B=Fe,Co,Ni,B?=Co,Ni,Mn)have been studied.The B and B?atoms are arranged in order along the[100]?[010]and[001]crystal directions,respectively.In order to determine the structure and magnetic configuration of different materials,all material calculations take into account three space groups and four different magnetic configurations to find the stable state of the material.The stability of the material was determined by calculating the formation energy,phonon spectrum and molecular dynamics simulation.For materials that are thermodynamically and kinetically stable,the calculation of the density of states can lead to the study of the electronic structure and magnetism of the material.Finally,the magnetic exchange coefficient is calculated by the Heisenberg model and the magnetic coupling mechanism of these stable materials is analyzed by the Goodenough-Kanamori rule.The results show that Sr₂Co_0.5Mn_1.5O₅ and Sr₂Ni_0.5Mn_1.5O₅ are stable ferromagnetic half-metallic materials with a band gap greater than 1e V,which means that they can achieve nearly 100%spin polarization even at high temperature,so they can be used in spintronics.It is hoped that this research will help to find new functional materials in calcium ferrite oxides.