Effect of chemical composition on superconductivity and magnetism in layered ruthenocuprates

Abstract

The ruthenium-based layered cuprates RuSr(2)GdCu(2)O(8) (RuGd1212) can be considered naturally occurring magnetic and superconducting multilayer systems. We have concentrated on the preparation of RuGd1212-type compounds with nominally stoichiometric composition under ambient pressure conditions. For small rare earth ions R = Gd, Eu (and Sm), single phase compounds are obtained with the typical ordered layered structure and no significant changes of physical properties. With large rare earth ions (R = Nd, Pr), multiphase samples are obtained. In these cases, no ordered layered structure was observed. The effect of substituting Sr(2+) with the smaller Ca(2+) and larger Ba(2+) is examined. A different number and different types of phases in equilibrium are found with different alkaline earths (A = Ca, Sr, Ba) at the nominal RuA(2)NdCu(2)O(8) composition. The variation in the mismatch of the A/Nd size does not lead to the formation of an ordered layered RuA(2)NdCu(2)O(8) compound. Chemical transport in an open system was used to vary the Ru content in the RuGd1212 samples during the annealing step. With an increase of the Ru mass transport to the sample, the composition can be driven beyond the limit of the homogeneity range. Systematic changes in the phase composition of the resulting sample were observed. The magnetic and superconducting transition temperatures vary in a systematic way and are attributed to a variation of the Ru content in the RuR1212 phase.

Magnetic, electrical and structural properties of the new Re-doped ruthenocuprate Ru1-xRexSr2GdCu2Oy

“…Isovalent substitution (Re 5+ ) in principle does not cause doping or hole extraction, but it substantially changes the overlapping of orbital d (Ru/Re) and 2p (O) when 4d of Ru is substituted for 5d of Re. However, this should be considered a mixed valence Ru 4+ (4d − t 2g 4 , S= 1) / Ru 5+ (4d − t 2g 3 , S= 3/2) which would lead to a doping with holes in the CuO 2 according to the relation Ru 5+ + Cu 2+ → Ru 5−δ + Cu 2+δ/2 [29].…”

The characteristics of the superconducting and magnetic phases in the polycrystalline samples of ruthenocuprates of nominal compositions RuSr2GdCu2O8, Ru0.98Sr2GdCu2O8 and Ru0.5Sr2GdCu2.5O8-d

“…The T c for Ru 1-x Sr 2 GdCu 2+x O 8-d , x>0, becomes dependent on the oxygen content [14], which resembles the well known oxygen content driven charge doping in the structurally related 123type superconducting cuprates. The process of formation of the RuSr 2 GdCu 2 O 8 was recently studied in the experiments in which the amount of the Ru ions available for synthesis was varied by differing arXiv:0905.1721v4 the chemical vapour transport of the Ru-oxides into the reaction zone [15,16]. The resulting materials revealed slight changes in the Ru/Cu ratio and for such a modified phase it was noted that the increase of T c associates a slight decrease in the Ru content.…”

“…The finite rate of diffusion of the Ru ions into the bulk, and simultaneous evaporative loss of the Ru atoms, were identified the two processes leading to different values of T c in the surface layer versus the core of the sample. Then, the material with homogeneous T c was reported by adjusting the efficiency of the chemical vapour transport [16]. In the associated investigation [17], for having established mixed valence, i.e.…”

Commentary on the superconducting and magnetic properties of the ruthenocuprates

“…It seemed therefore important to further investigate for the features, which control the superconducting T c , then only re-accessing twining of the compound superconductivity with its magnetism. Turning to solid state chemistry of the sintered samples of ruthenocuprates note here recently published investigation for the Ru sublimation processes, likely accompanying the high temperature reaction at oxidative conditions, which indicated differences in the Ru content in the bulk vs. surface of sintered RuSr 2 GdCu 2 O 8 and associated the effect to observed changes of T c [43] (for extensive review of related synthesis issues reported by the same group see Ref. [44]).…”