74 research outputs found
On the effect of heterovalent substitutions in ruthenocuprates
We discuss the properties of superconducting derivatives of the RuSr2GdCu2O8
(1212-type) ruthenocuprate, for which heterovalent doping has been achieved
through partial substitution of Cu ions into the RuO2 planes
(Ru1-xSr2GdCu2+xO8-d, 0<x<0.75, Tcmax=72 K for x=0.3-0.4) and Ce ions into the
Gd sites (RuSr2Gd1-yCeyCu2O8, 0<y<0.1). The measurements of XANES, thermopower,
and magnetization under external pressure reveal an underdoped character of all
compounds. Muon spin rotation experiments indicate the presence of magnetic
order at low temperatures (Tm=14-2 K for x=0.1-0.4). Properties of these two
series lead us to the qualitative phase diagram for differently doped 1212-type
ruthenocuprates. The difference in temperature of magnetic ordering found for
superconducting and non-superconducting RuSr2GdCu2O8 is discussed in the
context of the properties of substituted compounds. The high pressure oxygen
conditions required for synthesis of Ru1-xSr2RECu2+xO8-d, have been extended to
synthesis of a Ru1-xSr2Eu2-yCeyCu2+xO10-d series. The Cu->Ru doping achieved in
these phases is found to decrease the temperature for magnetic ordering as well
the volume fraction of the magnetic phase.Comment: Proceedings of the 3rd Polish-US Workshop on Magnetism and
Superconductivity of Advanced Materials, July 14-19, 2002, Ladek Zdroj
(Poland) to appear in Physica
Structural analysis, magnetic and transport properties of the (Ru1-xCox)Sr2GdCu2O8 system
The effects of Co substitution on structural and superconducting properties
of RuSr2GdCu2O8 compound have been studied. Rietveld refinements of the X-ray
diffraction patterns indicate that the cobalt ion progressively replaces
ruthenium sites. This replacement induces significant changes on the crystal
structure and on the magnetic and superconducting properties. The effects Co
substitution on the superconducting behaviour, and more particulary on the
changes induce by the hole doping mechanism, were investigated in
(Ru1-xCox)Sr2GdCu2O8 by a "bond valence sum" analysis with Co content from x=
0.0 to x = 0.2. The weak ferromagnetic transition at Tm= 138.2 K is shifted to
lower temperature, and suppressed at higher Co content. From the
crystallographic point of view the Ru-O(1)-Cu bond angle, associated to the
rotation of the RuO6 octahedra, around the c-axis remain essetially constant
when Ru is substituted by Co. Furthermore, increasing Co content has the effect
to increase the weak ferromagnetic moment, which may be interpreted as the main
responsible for breaking the delicate balance between magnetic and
superconducting ordering.Comment: 21 pages, 8 figure
Assessment of the relationship between genotypic status of a DT-diaphorase point mutation and enzymatic activity
DT-diaphorase, a cytosolic reductase, has been implicated as an activator of chemotherapeutic prodrugs and a detoxifier of certain potentially carcinogenic xenobiotics. A common C to T nucleotide 609 substitution in DT-diaphorase cDNA has been associated with protein instability and reduced catalytic activity. The degree to which the allelic status of the substitution correlates with enzymatic activity was assessed in 45 normal human skin fibroblast strains using a PCR-RFLP assay. Included in this study was the 3437T strain, which is unique in that it is heterozygous for the polymorphism yet contains undetectable enzymatic activity. An allele-specific RT-PCR-RFLP technique attributed this phenomenon to exclusive DT-diaphorase mRNA expression from the variant allele. Overlap in activities was observed between individual strains homozygous for the wild-type allele and heterozygotes, but the former group displayed enzymatic activity that was on average 2-fold higher. Western blot analysis of the two strains in this panel that are homozygous for the variant allele revealed that they express relatively low amounts of DT-diaphorase protein, consistent with the role of the substitution in protein instability. This work confirms that genotypic status is a reliable initial estimate of DT-diaphorase activity. © 2000 Cancer Research Campaig
AC losses and critical current density of superconducting GdBa2Cu3O7−x
Energy losses occurring in a cylindrical sample of Gd-Ba-Cu-O, subjected to an external AC magnetic field were examined. The loss dependence on the amplitude of the magnetic induction exhibits two stages of flux penetration into the superconductor. Critical current densitities for both stages of penetration were examined and an explanation for such behaviour is proposed. Support for this point of view is obtained by measurements on pulverized sample material. All measurements were performed at a temperature of 4.2 K and in absence of a background field.\ud
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Analysis of the data provides two critical current densities: an inter-granular critical current density at weak alternating magnetic fields and an intra-granular critical current density at higher magnetic fields. The intra-granular critical current density is at least two orders of magnitude larger than the inter-granular one
Synthesis effects on the magnetic and superconducting properties of RuSr2GdCu2O8
A systematic study on the synthesis of the Ru-1212 compound by preparing a
series of samples that were annealed at increasing temperatures and then
quenched has been performed. It results that the optimal temperature for the
annealing lies around 1060-1065 C; a further temperature increase worsens the
phase formation. Structural order is very important and the subsequent grinding
and annealing improves it. Even if from the structural point of view the
samples appear substantially similar, the physical characterization highlight
great differences both in the electrical and magnetic properties related to
intrinsic properties of the phase as well as to the connection between the
grains as inferred from the resistive and the Curie Weiss behaviour at high
temperature as well as in the visibility of ZFC anf FC magnetic signals.Comment: 17 pages, 12 figures. Proc. Int. Workshop " Ruthenate and
rutheno-cuprate materials: theory and experiments", Vietri, October 2001. To
be published on LNP Series, Springer Verlag, Berlin, C. Noce, A. Vecchione,
M. Cuoco, A. Romano Eds, 200
Study of the crystal structure, superconducting and magnetic properties of Ru1-xFexSr2GdCu2O8
Samples of the Ru1-xFexSr2GdCu2O8 system with x = 0, 0.025, 0.05, 0.075, 0.1
and 0.2, were prepared and their structural, superconducting and magnetic
properties were studied. Rietveld refinement of the X-ray diffraction patterns
show that the Fe substitution occurs in both Ru and Cu sites. An increase of Fe
concentration produces no significant changes in the bond angle Ru-O(3)-Ru,
which is a measure of the rotation of the RuO6 octahedra around the c-axis, and
also in the bond angle Ru-O(1)-Cu, which is a measure of the canting of the
RuO6 octahedra. On the other hand, the bond angle Cu-O(2)-Cu, which is a
measure of the buckling of the CuO2 layer, has a slight tendency to decrease
with the increase of the Fe content. We found thet both ferromagnetic and
superconducting transition temperatures are reduced with the increase of Fe
concentration. Analisys related to the decay of the superconducting and
ferromagnetic states is presented.Comment: 9 pages, 7 figure
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