| Perovskite compounds, which were discovered in the1960s, have recently attracted a great deal of interest in basic and applied research due to their extraordinary structure and a variety of exotic electronic properties that include a spectacular decrease of electrical resistance in a magnetic field, the effect of doping on the band of perovskite compounds. In recent years we have witnessed an increased interest in the study of transition metal oxides with an ordered double perovskite structure A2BB’O6(where A are alkaline earth elements Mg, Ca, Sr and Ba or rare earth elements La, Ce and Nd, B/B’ are heterovalent transition metal elements such as B=Cr, Mn, Fe, Co and Ni, B’=Mo, W and Re). Novel and attractive properties that can be useful in future spintronic device applications have been demonstrated, such as the large tunneling type magnetoresistance observed at room temperature, as well as the low field magnetoresistance found in Sr2FeReO6and Ba2FeReO6.In order to understand the electronic structure and magnetic exchange of the double perovskites in details, all the metallic/magnetic ions on the A, B and B’ sites as well as the electron doping studies have been intensive researched recently. There has been considerable work on the structural and magnetic properties on the Sr2FeReO6with the Cr, Nb and Ta doping. To the best of our knowledge, there is no report on the electronic structure and magnetic properties of the Tc-doped and Ba-doped Sr2FeReO6. In this paper, the structure, electronic and magnetic properties of Sr2-xBaxFeReO6(x=0to2) have been studied by using the projector augmented wave potentials under generalized gradient approximation. All of the compounds are insulators in one of the spin channels, but a metal in the other. This leads to a complete spin polarization at the Fermi level and thus application as a source of spin polarized charge carriers in spintronic devices. The following conclusions are obtained:1) The results show that the cell volume shrinks as Tc concentration increases, while the lattice parameters have no obvious change. That results from the sites and the smaller ionic size of the Tc ions in the Sr2FeRe1-xTcxO6.2) The Sr2FeRe1-xTcxO6holds the same ferromagnetic groundstate as the undoped Sr2FeReO6. And the local magnetic moments of Fe ions increases from3.705μB to 3.794μB with the Tc doping, while the local magnetic moments of Re (Tc) ions decreases from-0.864μB (-1.495μB) to-0.288μB (-1.063μB) with the Tc doping. Therefore, doping Tc ions leads to a reduction in the Sr2FeRe1-xTcxO63) The total magnetic moments, and the reduction has an increased tend with increasing the Tc ions component (x) in the Sr2FeRe1-xTcxO6.4) These Sr2FeRe1-xTcxO6systems are half-metallic and could be used in the field of quasi-one-dimensional spintronics devices for producing100%spin polarized currents. More important, each Sr2FeRe1-xTcxO6with different x also has half-metallic character, this is to say, the half-metallic nature is not destroyed when doping Tc ions, and it has no relationship to the different x.5) More charges are accumulated around O atoms reflecting substantial charge transfer from Re and Fe atoms to O atoms. And the charge distributions show that there exists no direct interaction between two nearest Fe-Fe, Re-Re, Tc-Tc pairs, whereas along each Fe-O-Re-O-Fe chain or Fe-O-Tc-O-Fe chain, the hybridizations between Fe3d, O2p, and Re5d or Tc4d orbitals are fairly significant.6) For Sr2-xBaxFeReO6(x=0,0.25,0.50,0.75,1.00,1.25,1.50,1.75,2), all these systems are half-metallic and could be used in the field of spintronics devices for producing100%spin polarized currents.7) The band gap of the total spin-up DOS at the Fermi level increases slightly with increasing the x for Sr2-xBaxFeReO6and can be adjusted by change the content of the Ba.8) The total magnetic moments of the Sr2-xBaxFeReO6increase from3.0325μB to3.μB with the Ba doping except for x=1.25.9) It can be seen that Ba and O atoms have stronger interaction than Sr and O atoms. And the interaction of Fe and O atoms is stronger in Sr2FeReO6than that in Ba2FeRe06. |
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