C. W. Chu

A possible crypto-superconducting structure in a superconducting ferromagnet

Abstract We have measured the dc and ac electrical and magnetic properties in various magnetic fields of the recently reported superconducting ferromagnet RuSr2GdCu2O8. Our reversible magnetization measurements demonstrate the absence of a bulk Meissner state in the compound below the superconducting transition temperature. Several scenarios that might account for the absence of a bulk Meissner state, including the possible presence of a sponge-like nonuniform superconducting or a crypto-superconducting structure in the chemically uniform Ru-1212, have been proposed and discussed.

Magnetic field effect and dielectric anomalies at the spin reorientation phase transition of GdFe 3 (BO 3 ) 4

GdFe3(BO3)4 exhibits a structural phase transition at 156 K, antiferromagnetic order of the Fe3+ moments at 36 K followed by a spin reorientation phase transition at 9 K. The reorientation phase transition is studied through dielectric, magnetic and heat capacity measurements under the application of external magnetic fields of up to 7 kOe. The dielectric constant indicates the existence of two distinct anomalies at T_SR = 9 K that separate in temperature under external magnetic fields. The spin rotation phase transition is proven to be of the first-order nature through the magnetic analogue of the Clausius-Clapeyron equation. Magneto-dielectric effect of up to 1% is observed at 8 K and 7 kOe. The uniaxial magnetocaloric effect along the c axis is observed below the spin reorientation phase transition of 9 K.

Evidence for polaronic Fermi liquid in manganites

The modern multipolaron theory predicts a polaronic Fermi-liquid state, but such a state has not been unambigously confirmed by experiment so far. Here we report theoretical and experimental studies of the isotope effects on the low temperature kinetic properties of the doped ferromagnetic manganites. Our results provide clear evidence for a polaronic Fermi-liquid state in doped ferromagnetic manganites.

Study of binary and pseudo-binary intermetallic compounds with AlB2 structure

Abstract We have synthesized and studied the binary intermetallic compounds, AGa2 and A[GaxSi2−x] (A=Sr, Ba, Ca), which are isostructural to the newly discovered 40 K superconductor MgB2. The binary compounds AGa2 were found to be non-superconducting above 2 K, even though they have the same valence electron number per formula as MgB2 and greater lattice parameters than MgB2. However, by varying the valence electron number, they become superconducting. This result suggests that the electronic structures of this class of compounds depend on more than just the valence electron density and the lattice parameters. The theoretical prediction that the Tc of MgB2 could be enhanced with the proper dopant to increase its carrier density or to expand the lattice could not be verified.

Pressure effects on strained FeSe0.5Te0.5 thin films

The pressure effect on the resistivity and superconducting Tc of prestrained thin films of the iron chalcogenide superconductor FeSe0.5Te0.5 is studied. Films with different anion heights above the Fe layer showing different values of ambient pressure Tc’s are compressed up to a pressure of 1.7u2009GPa. All films exhibit a significant increase of Tc with pressure. The results cannot solely be explained by a pressure-induced decrease of the anion height but other parameters have to be considered to explain the data for all films.

Origin of the superconductivity in the Y-Sr-Ru-O and Y-Sr-Cu-O systems

We report on the structural, magnetic, and Raman-scattering studies of double-perovskite structure

High temperature superconducting materials: Present status, future challenges, and one recent example—the superconducting ferromagnet

{mathrm{Sr}}_{2}mathrm{Y}{mathrm{Ru}}_{1ensuremath{-}x}{mathrm{Cu}}_{x}{mathrm{O}}_{6ensuremath{-}ensuremath{delta}}

Magnetic phase diagram and magnetoelectric properties of Ho0.25Nd0.75Fe3(BO3)4

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

Separation between antiferromagnetic and ferromagnetic transitions in Ru 1 − x Cu x Sr 2 EuCu 2 O 8 + δ

{mathrm{Sr}}_{2}mathrm{Y}mathrm{Ru}{mathrm{O}}_{6}

Generation of negative capacitance in a nanocolloid

has been observed only for partially melted ceramic materials. We show that superconductivity is associated with the 1:2:3 phase