Possible ordering of Ru and Cu in the charge-reservoir of magneto-superconductor RuSr2GdCu2O8 (Ru-1212): Magnetic, transport, and TEM microstructural studies

Abstract

Magnetization vs temperature behavior of RuSr2GdCu2O8−δ (Ru-1212) measured in an field of 5 Oe, shows a clear branching of zero-field-cooled (ZFC) and field-cooled (FC) curves around 140 K, a cusp at 135 K, and a diamagnetic transition around 20 K (in the ZFC branch). The cusp at 135 K is due to the antiferromagnetic ordering of the Ru moments. The magnetization-field isotherms, below 50 K, show a nonlinear contribution from a ferromagnetic component. The resistance vs temperature behavior of the compound, in applied fields of 0, 3, and 7 T, confirms that the sample is superconducting at around 20 K. The superconducting transition exhibits field broadening of a type different than that known for conventional high Tc superconductors. The magnetoresistance (MR) is negative above the Ru magnetic ordering temperature of 135 K, while below this temperature, MR displays a positive peak in low fields and becomes negative in higher fields. A maximum of 2% is observed for the negative MR value at the Ru magnetic ordering temperature. An electron diffraction pattern obtained for this Ru-1212 sample shows two types of superstructure; one with a weak spot at the center of the a–b rectangle and the other only along the b direction. It is possible that either Ru/Cu or Ru4+/Ru5+ ordering of 2b periodicity takes place along the b direction.

Magneto-superconductivity of 100-atm O2-annealed RuSr2Gd1.5Ce0.5Cu2O10−δ

“…Coexistence of superconductivity and magnetism in ruthenium copper oxides was reported for the first time for RuSr2(Gd,Sm,Eu)1.6Ce0.4Cu2O10-δ [Ru-1 (Sr) 2 (Gd,Sm ,Eu,Ce) 22 or Ru-1222] [1,2], and later for Ru-1 (Sr) 2 (Gd) 12 (Ru-1212) [3][4][5].…”

“…Both Ru-1222 and Ru-1212 phases are structurally related to the In the Ru-1222 structure furthermore, a three-layer fluorite-type block instead of a single oxygen-free R (= rare earth element) layer is inserted between the two CuO2 planes of the Cu-1212 structure [7]. In both Ru-1222 and Ru-1212 replacement of Cu in the charge-reservoir block by the higher -valent Ru increases the overall oxygen content [1][2][3][4][5].…”

“…Both ruthenium copper oxides were synthesized and studied for their transport propert ies already in 1995 [6] , but magnetic characterization had not been carried out until recently [1][2][3][4][5]. Both Ru-1222 and Ru-1212 phases are structurally related to the In the Ru-1222 structure furthermore, a three-layer fluorite-type block instead of a single oxygen-free R (= rare earth element) layer is inserted between the two CuO2 planes of the Cu-1212 structure [7].…”

Magneto-Superconductivity of Rutheno-Cuprates

“…Interestingly in presently studied nonsuperconducting RuSr 2 GdCu 2 O 8-δ samples the ordering temperature of Ru moments appears to be 13 K higher than the value reported for similar but superconducting samples [8,15,33]. Both the ZFC and FC branching about 145 K and the sharp peak at 2.6 K are seen for all the samples including the high-O2-pressure annealed and the argon annealed ones.…”

“…Furthermore, as already assumed based on the lattice parameters and the Tc values, the difference between the 100-atm and 1-atm O2-annealed samples is larger for the Ru-1222 phase than for the Ru-1212 phase, see also the data for relevant samples in Refs. [25,33,34]. In Table 1 As far as the HTHT treated various Ln/Ru-1212, 1222 or 1232 compounds are concerned their oxygen stoichiometry is believed to be very close to nominal, because nearly no change was observed in the weight of synthesized samples, indicating towards their fixed nominal oxygen content.…”