New structure in the REBaCuFeO sub(5+ delta ) series: LaBaCuFeO sub(5+ delta ). Structure and magnetic properties in the La sub(1-x)Pr sub(x)BaCuFeO sub(5+ delta ) system

摘要

The crystal structure of LaBaCuFeO sub(5+ delta ) is determined by neutron powder diffraction at 15 K and the structure and magnetic properties of the La sub(1-x)Pr sub(x)BaCuFeO sub(5+ delta ) system are studied by AC-susceptibility measurements and RT super(57)Fe Moessbauer spectroscopy. The best fit using the Rietveld method is obtained for an orthorhombic model in space group I mmm with unit cell parameters a identical with 5.5586(8) angstroms, b identical with 5.5550(9) angstroms and c identical with 7.8155(2) angstroms. The main feature of this model is a disordered structure where the oxygen atom vacancies play an important role. The magnetic susceptibility in the La sub(1-x)Pr sub(x)BaCuFeO sub(5+ delta ) system is studied and T sub(f), mu sub(eff) and theta are determined. Moessbauer spectra provide information relative to the iron electronic state and environment. They support the hypothesis of the key role that the oxygen atom positions play in the magnetic properties of the system by affecting the superexchange interactions in the network.