Studies Of Crystal Structure And Magnetism Of Doped SrFeO_3-δ And SrFeO₂

Abstract:Perovskite and layered oxide are of great interest because of their unique and technologically useful properties. We studies the crystal structure and magnetism of the perovskite Sr1-xAxFeO3-δ(A=Ba,Ca) and SrFe1-xBxO3-δ(B=Cu,Co)(x=0,0.1,0.2,0.3), as well as the infinite-layered Sr1-xBaxFeO2and SrFe1-xBxO2(B=Cu,Co)(x=0,0.1,0.2,0.3). This paper is structured as follows:(1) The nonstoichiometric perovskite Sr1-xAxFeO3-δ(A=Ba,Ca) are prepared using sol-gel method. The XRD and Rietveld refinement show that the samples shift from the tetragonal structure to a cubic structure. Sr1-xAxFeO3-δ(A=Ba,Ca)(x=0.1,0.2,0.3) are cubic structure with a space group of Pm3m, and the lattice constant increase with Ba, but decrease gradually with Ca. The magnetic measurement show that Sr1-xBaxFeO3-δ exhibit a transition from an antiferromagnetic state to a ferromagnetic state at extremely low temperature, and Sr0.7Ca0.3FeO3-δ exhibits a transition from an antiferromagnetic to a ferromagnetic state, but the other samples are antiferromagnetic.(2) The nonstoichiometric perovskite SrFe1-xBxO3-δ(B=Cu,Co) are prepared using sol-gel method. The XRD and Rietveld refinement show that SrFe1-xCuxO3-δ(x=0.1,0.2,0.3) are cubic structure, and and the lattice constant decrease with Cu; But SrFe1-xCoxO3-δ(x=0,O.1,0.2,0.3) shift from the tetragonal structure to a cubic structure when the content of Co exceed20%. The magnetic measurement show that SrF1-xCuxO3-δ are antiferromagnetic. Although the transition temperature of the samples x=0.1,0.2,0.3is lower than the sample x=0, it increase with the Cu, and the effective magnetic moment reduce with Cu. However, SrFe1-xCoxO3-δ(x=0.1,0.2,0.3) exhibit a transition from an antiferromagnetic state to a ferromagnetic state.(3)The quasi two-dimensional infinite layered structure Sr0.9Ba0.1Fe02、SrFe1-xCuxO2(x=0.1,0.2) and SrFe1-xCoxO2(x=0,0.1,0.2,0.3) are prepared by low temperature solid-state reaction, which are tetragonal structure with a space group of P4/mmm. With the increase of doping concentration, reaction time increased, and the thermal stability reduced. The magnetic measurement show that SrFeO2is antiferromagnetic with the Neel temperature of533K, which is consistent with the result of the neutron diffraction. But the preparation of SrFeO2and its doping system is easy to introduce ferromagnetic impurity phase, which lead to the hardship of the intrinsic magnetic macro test.