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This paper reports progress in the development of COMB magnet technology with STAR wires. A two-layer dipole magnet with 60 mm clear bore has been recently fabricated and tested in liquid nitrogen. The purpose of the test was to determine what kind of critical current degradation occurs in the process of winding the STAR wire into the COMB structure., Comment: CEC/ICMC23

At zero magnetic field, a series of five phase transitions occur in Co3V2O8. The Neel temperature, TN=11.4 K, is followed by four additional phase changes at T1=8.9 K, T2=7.0 K, T3=6.9 K, and T4=6.2 K. The different phases are distinguished by the commensurability of the b-component of its spin density wave vector. We investigate the stability of these various phases under magnetic fields through dielectric constant and magnetic susceptibility anomalies. The field-temperature phase diagram of Co3V2O8 is completely resolved. The complexity of the phase diagram results from the competition of different magnetic states with almost equal ground state energies due to competing exchange interactions and frustration., Comment: Proceedings of the 2007 Conference on Strongly Correlated Electron Systems, 2 pages, 2 figures

The magnetic phase diagrams of RMnO3 (R = Er, Yb, Tm, Ho) are investigated up to 14 Tesla via magnetic and dielectric measurements. The stability range of the AFM order below the Neel temperature of the studied RMnO3 extends to far higher magnetic fields than previously assumed. Magnetic irreversibility indicating the presence of a spontaneous magnetic moment is found near 50 K for R=Er, Yb, and Tm. At very low temperatures and low magnetic fields the phase boundary defined by the ordering of the rare earth moments is resolved. The sizable dielectric anomalies observed along all phase boundaries are evidence for strong spin-lattice coupling in the hexagonal RMnO3. In HoMnO3 the strong magnetoelastic distortions are investigated in more detail via magnetostriction experiments up to 14 Tesla. The results are discussed based on existing data on magnetic symmetries and the interactions between the Mn-spins, the rare earth moments, and the lattice., Comment: 23 pages, 16 figures, to be published in JMR's Aug. focus issue on multiferroics

We report on the structural, magnetic, and Raman-scattering studies of double perovskite structure Sr2Y(Ru1-xCux)O6-d systems made by systematic synthesis processes with various numbers of doping concentrations and sintering temperatures. We observed different behaviors resulting from the different thermal treatments. In particular, superconductivity in Cu-doped Sr2YRuO6 has been observed only for partially melted ceramic materials. We show that superconductivity is associated with the 1:2:3 phase (YSr2Cu3Ot), similar to that of Y-Sr-Cu-O samples sintered at high temperature.

Two magnetic transitions are observed in the magneto-superconducting RuEu2-xCexSr2Cu2O10 (Ru-1222), at TM 160 K and TM2~80 K. Below TM2 the Ru moments are weak-ferromagnetically ordered and wide ferromagnetic hysteresis loops are observed, they become narrow and disappear at ~ 60-70 K. Above TM2, (i) small antiferromagnetic-like hysteresis loops reappear with a peak in the coercive fields around 120 K. (ii) A small peak at ~120 K is also observed in the dc and ac susceptibility curves. The two phenomena are absent in the non-SC x=1 samples. For x<1, the decrease of the Ce4+ content, is compensated by non-homogeneous oxygen depletion, which may induce a reduction of Ru5+ ions to Ru4+. The higher ordering temperature, TM, which does not change with x, may result from Ru4+ rich clusters, in which the Ru4+-Ru4+ exchange interactions are stronger than the Ru5+-Ru5+ interactions. In the superconducting Ru1-xMoxSr2Eu1.5Ce0.5Cu2O10 (x=0-0.4) system, TM2 shifts to low temperature with x (14 K for x=0.4), whereas TM is not affected by the Mo content, indicating again that TM may not correspond to the main phase. Two scenarios are suggested to explain the magnetic phenomena at TM2

The results of micro-structural and detailed magnetization studies are reported here for our recently published TbSr2Cu2.7Mo0.3O7+d superconductor with a transition temperature (Tc) at as high as 80 K [1]. From XRD and EDX the sample was confirmed to be of single-phase and possess the nominal cation stoichiometry. The SEM images showed well-developed grains for this ceramic high-Tc superconductor. Magnetization measurements at various temperatures and fields revealed bulk superconductivity below 80 K. Magnetization versus applied field (M vs. H) loops at various temperatures below the Tc exhibited clear full penetration field HP. In normal state (> 100 K) the susceptibility follows the Curie-Weiss behavior with an effective paramagnetic moment of 9.83 mB., Comment: 11 pages of text and figs. Accepted in Physica C

The properties of the MoSr2RCu2O8 (R=rare earth) system are found to systematically change with the contraction of the R ions. For the light R ions (La-Nd) the samples are paramagnetic down to 5 K, whereas in the intermediate range (Sm-Tb), the Mo sublattice orders antiferromagnetically at TN, ranging from 11 to 24 K. For the heavy R ions, Ho-Tm and Y, superconductivity appears at TC in the range 19-27 K and antiferromagnetism sets in at TN < TC. This latter behavior resembles most of the magneto-superconductors, but is in sharp contrast to the iso-structural RuSr2RCu2O8 system where TN > TC.

The properties of the MoSr2YCu2O8 materials are found to systematically change with the oxygen concentration determined by the sintering and annealing conditions. The as-prepared (asp) sample is anti-ferromagnetically (AFM) ordered at 16 K. The magnetic features are related to the Mo5+ sublattice. Annealing under an oxygen atmosphere induces superconductivity (SC) in the Cu-O planes, and the TC and the shielding fraction values obtained depend strongly on the oxygen concentration. Annealing the asp material at 1030 C under ambient oxygen atmosphere yields TC of 18 K, whereas further annealing at 650 C under 92 atm. of oxygen, shifts TC to 32 K. The AFM ordering, which coexists with SC state through effectively decoupled subsystems, is not affected by the presence or absence of the SC state. In all samples studied, TN < TC. This behavior resembles most of the inter-metallic magneto-superconductors, but is in sharp contrast to the iso-structural RuSr2GdCu2O8 system where TN > TC., Comment: 7 pages, 8 Figures

RuY1.5Ce0.5Sr2Cu2O10, is not superconducting (SC) and orders magnetically at TM =152 K. The Ru moment at 5K is 0.75 mB. Ferromagnetic hysteresis loops are observed below Tirr= 100 K. At 100 K, the remanent magnetization (Mrem) and the coercive field (HC) become zero. Surprisingly, at Tirr

We have investigated the MoSr2R1.5Ce0.5Cu2O10-d (Mo-1222R, R=rare earth) system by several complementary experimental techniques. In contrast to the iso-structural RuSr2R1.5Ce0.5Cu2O10-d (Ru-1222) system, in which superconductivity (SC) in the CuO2 planes and weak-ferromagnetism in the Ru sub-lattice coexists, in Mo-1222, displays a competition between the two states, namely, SC vanishes when the magnetic order sets in. The contraction in the R elements leads to a change of the physical states. The light R ions (Pr and Nd) are paramagnetic down to 5 K, whereas the middle R ions (Sm and Eu) are SC at TC 18-23 K respectively. The SC charge carriers originate from the CuO2 planes, and annealing under oxygen pressures does not affect TC. A simple model for the SC state is proposed. For the heavy R elements Ho-Lu and Y, the pentavalent Mo layers are antiferromagnetically (AFM) ordered at TN ranging from 13-26 K. For R=Gd, the sample is not SC and exhibit two magnetic transitions at 11 and 184 K. Both the SC or AFM states depend strongly on the R/Ce ratio and for R/Ce=1, both states are suppressed., Comment: 4 pages, 4 figures, submitted to PRB

Eu2-xCexRuSr2Cu2O10-d (Ru-2122) is the first Cu-O based system in which superconductivity (SC) in the CuO2 planes and weak-ferromagnetism (W-FM) in the Ru sub-lattice coexists. The hole doping in the CuO2 planes, is controlled by appropriate variation of the Ce concentration. SC occurs for Ce contents of 0.4-0.8, with the highest TC=35 K for Ce=0.6. The as-prepared non-SC EuCeRuSr2Cu2O10 (x=1) sample exhibits magnetic irreversibility below Tirr=125 K and orders anti-ferromagnetically (AFM) at TM =165 K. The saturation moment at 5 K is Msat=0.89 mB /Ru close to the expected 1 mB for the low-spin state of Ru5+. Annealing under oxygen pressures, does not affect these parameters, whereas depletion of oxygen shifts both Tirr and TM up to 169 and 215 K respectively. Systematic magnetic studies on Eu2-xCexRuSr2Cu2O10-d show that TM, Tirr and Msat decrease with x, and the Ce dependent magnetic-SC phase diagram is presented. A simple model for the SC state is proposed. We interpret the magnetic behavior in the framework of our ac and dc magnetic studies, and argue that: (i) the system becomes AFM ordered at TM; (b) at Tirr < TM, W-FM is induced by the canting of the Ru moments, and (c), at lower temperatures the appropriate samples become SC at TC. The magnetic features are not affected by the SC state, and the two states coexist., Comment: submitted to Physical Review B