D.Y. Chen

Magnetism and superconductivity in Sr \(\)YRu \(\)Cu \(\)O \(\) and magnetism in Ba \(\)GdRu \(\)Cu \(\)O \(\)

Abstract:We report magnetization, surface resistance (), and electron spin resonance (ESR) for non-superconducting Ba2GdRu1-uCuuO6, and find that all three magnetic ions (Gd, Ru, and Cu) are ordered at low temperatures. Both ESR (Gd sublattice) and weak ferromagnetic resonance (dopant Cu) are observed, while no magnetic resonance due to either paramagnetic or ordered Ru is detected. In addition, for superconducting ( K) Sr2YRu1-uCuuO6, resistivity, muon spin rotation (SR), and 99Ru Mössbauer absorption are reported. None of the O6 materials (e.g., Sr2YRu1-uCuuO6) have cuprate planes, although Cu is employed as a dopant. In Sr2YRu1-uCuuO6, the Ru moments order at a temperature (23 K) below that for the resistive onset of superconductivity, while the Cu orders at a higher temperature, 86 K. Therefore at low temperatures, this material exhibits magnetic order, coexisting with diamagnetism. The only non-magnetic layers in the superconducting O6 structure, the SrO layers, carry holes and exhibit diamagnetic screening characteristic of type-II superconductivity.

MUON SPIN ROTATION IN SR2YRU1-UCUUO6

The magnetic and superconducting behaviors of sintered Sr{sub 2}YRu{sub 1{minus}u}Cu{sub u}O{sub 6} (for u = 0.05, 0.10, 0.15) were probed using transverse- and zero-field muon spin rotation ({mu}{sup +}SR). In general, positive muons are attracted to oxygen ions in the high-{Tc} oxides, and so, Sr{sub 2}YRu{sub 1{minus}u}Cu{sub u}O{sub 4} layers and those associated with the SrO-layer oxygen. The transverse- and zero-field data for all three stoichiometries u exhibit a sudden onset of magnetic structure at T{sub N} {approximately} 30 K, with a static local field of {approximately}3 kG. This transition is marked by a dramatic increase in the relaxation rate as the temperature decreases below T{sub N}, corresponding to an increased static disordering of the magnetic moments. Above T{sub N} no static fields are observed. Instead the data exhibit a slow dynamic depolarization, presumably due to the rapid fluctuation of paramagnetic moments. Both transverse- and zero-field data also indicate a smaller second component ({approximately}10%) which the authors associate with the SrO layer, exhibiting superconducting behavior in transverse field with an observed {Tc} {approx} T{sub N} {approximately} 30 K.The magnetic and superconducting behaviors of sintered Sr2YRu1-uCuuO6 (for u=0.05, 0.10, 0.15) were probed using transverse- and zero-field muon spin rotation (μ+ SR). In general, positive muons are attracted to oxygen ions in the high-Tc oxides, and so, Sr2YRu1-uCuuO6 should (and does) present two types of μ+ sites, those associated with the oxygen in the YRuO4 layers and those associated with the SrO-layer oxygen. The tranverse- and zero-field data for all three stoichiometries u exhibit a sudden onset of magnetic structure at TN~30 K, with a static local field of ~3 kG. This transition is marked by a dramatic increase in the relaxation rate as the temperature decreases below TN, corresponding to an increased static disordering of the magnetic moments. Above TN no static fields are observed. Instead the data exhibit a slow dynamic depolarization, presumably due to the rapid fluctuation of paramagnetic moments. Both transverse- and zero-field data also indicate a smaller second component (~10%) which we associate with the SrO layer, exhibiting superconducting behavior in transverse field with an observed Tc≈TN~30 K.

Magnetism and superconductivity in Sr2A(Ru1−xCux)O6 (A=Y, Ho) system

Abstract We have synthesized a series of Cu-doping Sr2A(Ru1−xCux)O6 compounds, where A=Y or Ho. We observed superconducting transition in samples with x>0.04. In addition, magnetic orders at a temperature close to that of the superconducting transition, are present in the samples. There is an additional magnetic order at about 15 K in Ho samples. Detailed magnetic measurements suggest that this 15 K transition is ferromagnetic in nature, presumably due to Ho order. The observed striking features can be understood in terms of a model based on the double exchange mechanism, which occurs via Ru5+ spin coupling to itinerant electrons hopping between Ru-site.

NOVEL MAGNETISM AND SUPERCONDUCTIVITY IN A Ru-BASED DOUBLE PEROVSKITE

We report the observations, using magnetic susceptibility and specific heat measurements, of the coexistence of superconductivity and magnetic ordering at low temperatures in the Cu-doping double perovskites Sr2ARu1-xCuxO6, with A=Y or Ho, and x<0.2. The observed striking features can be understood in terms of a plausible theoretical model based on the double exchange mechanism, which occurs indirectly via Ru5+ spin coupling to itinerant electrons hopping from one Ru site to another.

Location and properties of the superconducting hole-condensate in Sr2YRu1−uCuuO6☆

Abstract The superconductivity in the compound Sr 2 YRu 1−u Cu u O 6 is in the SrO layers.

Magnetic resonance and surface resistance of Ba2GdRu1-uCuuO6

Abstract Using susceptibility and surface resistance measurements of Ba2GdRuO6 and of Ba2GdRu1−uCuuO6, we find that Gd, Ru, and Cu order antiferromagnetically at ∼12.5K, ∼48K, and ∼86K, respectively. The Gd electron spin resonance is exchange-narrowed by paramagnetic Ru, and is broadened to near-undetectability below TN(Ru)=48K. Ru fails lto resonate at all. Antiferromagnetic Cu exhibits a microwave frequency resonance at low fields.