STUDIES ON THE SYNTHETIC, STRUCTURAL, ELE CTRICAL AND MAGNETIC-PROPERTIES OF LN(N)MCO(N)O(3N+1) (LN=SM, GD, M=SR, BA, N=1,2)

Three new oxides Sm2SrCo2O7, Sm2BaCo2O7 and Gd2SrCo2O7 have been synth esized successfully by solid state reaction mathod. The X-Ray diffract ion spectra show that they are all isostructural with Sr3Ti2O7, and Ln (2)SrCo(2)O(7)(Ln=Sm,Gd) crystallized in tetragonal system, Sm2BaCo2O7 in orthrhombic system. The Co-O bonds in CoO2 planes of Ln(2)SrCo(2)O (7) are shorter than those of LnSrCoO(4)(Ln=Sm, Gd), and so their dele ctrons are more delocalized and their electrical resistivities are sma ller. The electrical resistivities versus temperature in the range 300 similar to 1100K showed that the five brides show the characters of w eakly localized systems. In the lower temperature range, the magnetic behaviors of Gd2SrCo2O7 and GdSrCoO4 fit Curie-Weiss law well, and the magnetic exchange reaction in CoO2 sublattices of Gd2SrCo2O7 is ferro magnetic, but that of GdSrCoO4 is antiferromagnetic. The other three o xides with Sm3+ showed complex magnetic behaviors which is perhaps rel ated with the complexity of Sm3+.