First-principles study of the structural, electronic, and magnetic properties of double perovskite Sr_2FeReO_6 containing various imperfections

The structural, electronic, and magnetic properties of double perovskite Sr_2FeReO_6 containing eight different imperfections of FeReor ReFeantisites, Fe1–Re1 or Fe1–Re4 interchanges, V_（Fe）, V_（Re）, VOor V_（Sr） vacancies have been studied by using the first-principles projector augmented wave（PAW） within generalized gradient approximation as well as taking into account the on-site Coulomb repulsive interaction（GGA＋U）. No obvious structural changes are observed for the imperfect Sr_2FeReO_6 containing FeReor ReFeantisites, Fe1–Re1 or Fe1–Re4 interchanges, or VSrvacancy defects. However, the six（eight） nearest oxygen neighbors of the vacancy move away from（close to） VFeor V_（Re）（VO） vacancies. The half-metallic（HM） character is maintained for the imperfect Sr_2FeReO_6 containing FeReor ReFeantisites, Fe1–Re4 interchange, V_（Fe）,VO or V_（Sr） vacancies, while it vanishes when the Fe1–Re1 interchange or VRevacancy is presented. So the Fe1–Re1 interchange and the VRevacancy defects should be avoided to preserve the HM character of Sr_2FeReO_6 and thus usage in spintronic devices. In the FeReor ReFeantisites, Fe1–Re1 or Fe1–Re4 interchanges cases, the spin moments of the Fe（Re）cations situated on Re（Fe） antisites are in an antiferromagnetic coupling with those of the Fe（Re） cations on the regular sites. In the V_（Fe）, V_（Re）, VO, or V_（Sr） vacancies cases, a ferromagnetic coupling is obtained within each cation sublattice,while the two cation sublattices are coupled antiferromagnetically. The total magnetic moments μtot（μB/f.u.） of the imperfect Sr_2FeReO_6 containing eight different defects decrease in the sequence of VSrvacancy（3.50）, VRevacancy（3.43）,FeReantisite（2.74）, VOvacancy（2.64）, VFevacancy（2.51）, ReFeantisite（2.29）, Fe1–Re4 interchange（1.96）, Fe1–Re1interchange（1.87）, and the mechanisms of the saturation magnetization reduction have been analyzed.