[en] We observed high magnetic field de Haas-van Alphen signals up to 57 T at low temperatures down to 0.5 K in the intermediate valence compound YbAl₃. High-field magnetization and magnetic susceptibility measurements imply that new electronic states in YbAl₃ are created with an energy scale of 40 K. In the <1 1 1> direction, the effective masses, which are 13.5m₀ for the α-branch and 23.9m₀ for the β-branch at low magnetic fields (<40 T), are strongly reduced to 5.25m₀ for both branches at high magnetic fields (>40 T)

[en] The spacing of the twins present in Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-δ/ has been investigated using optical and Transmission Electron Microscopy (TEM). Studies have reported that the value of the average twin spacing obtained by optical measurements is much larger than that measured in thin foils prepared for TEM observation, and controversy exists as to the exact nature of the optical twins. Experiments have been conducted which show that the twins observed optically correspond to those seen using TEM and are not produced by an optical interference effect. Using electron channeling, equations have been formulated which allow optical determination of the true spacing of twins present in a selected grain as well as the orientation of that grain. The average twin spacing measured in TEM has been found to vary with sample preparation method, being smaller for crushed chip samples than for bulk samples prepared by ion milling or jet-polishing. A variation of the twin spacing with grain size has also been noted

[en] The local structure around Sn dopants in CeCoIn_5-xSn_z has been probed by extended x-ray absorption fine structure (EXAFS) technique. The fit results for both x = 0.12 and x = 0.18 clearly indicate the dopant Sn atoms predominantly occupying the planar In(1) site. These results are consistent with the quasi-two-dimensional electronic properties of CeCoIn₅ and is discussed in relation to the observed bulk properties

[en] Using the concepts of ''Comparative crystal chemistry'', utilized by Hazen and Finger for insulating oxides, we have developed a model to estimate the anisotropic compressibility of high temperature superconductors. This model yields volume compressibilities within 10% of the accurate experimental values found by neutron diffraction on the superconducting oxides and accounts approximately for their compressibility anisotropy. In this model, the cation-anion coordination polyhedra, which themselves have different volumes and compressibilities, are considered. The compressibility of the bulk sample is then estimated by evaluating the compressibility of the individual layers in the layered structure. Estimates are made for the anisotropic compressibility of a large number of high temperature superconductors, including the many, like the electron-doped systems, whose compressibility has not yet been determined experimentally. (orig.)

[en] We have used high pulsed magnetic fields to 50 T to observe de Haas - van Alphen oscillations in the heavy fermion antiferromagnet UCd₁₁, which has a stongly enhanced value of the electronic specific-heat coefficient (γ=803 mJ/molK²). The low-temperature magnetization shows the existence of two magnetic phase transitions. The presence of quantum oscillations above the first transition indicates that UCd₁₁ has a coherent Fermi liquid, although there is little or no change in the Fermi-surface topology on passing through the second transition. copyright 1999 The American Physical Society

[en] A melt-annealing method has been developed to deposit highly textured superconducting thick films on different substrates in the Bi-Sr-Ca-Cu-O system. As opposed to previous techniques, this method uses powder made from an extremely dense glass sample to yield very uniform and dense thick films. The x-ray diffraction and scanning electron microscopy results indicate that the superconducting phase is strongly oriented along the c axis perpendicular to the substrate and the films are chemically uniform. Electrical transport measurements consistently show a T_c near 80 K for all samples

[en] We measured magnetic relaxation for the zero-field-cooled magnetization of liquid-quenched Bi-Sr-Ca-Cu-O samples with various microstructures at an applied field of 1 kOe. We found that a large amount of crystal defects observed in the sample matrix greatly increase the pinning strength and, in turn, enhance the flux-creep behavior. The relaxation rate peaks at 14 K and drops to zero near 60 K. The increased activation energy in our crystallized samples is attributed to strong pinning caused by a high density of precipitates and lattice stacking faults

No abstract available

[en] We have studied the spin relaxation in diluted spin ice Ho_2-x Y_x Ti₂O₇ by means of neutron spin echo spectroscopy. Remarkably, the geometrical frustration is not relieved by doping with non-magnetic Y, and the dynamics of the freezing is unaltered in the spin echo time window up to x ≅ 1.6. At higher doping with non-magnetic Y (x (ge) 1.6) a new relaxation process at relatively high temperature (up to at least T ≅ 55 K) appears which is more than 10 times faster than the thermally activated main relaxation process. We find evidence that over the whole range of composition all Ho spins participate in the dynamics. These results are compared to a.c. susceptibility measurements of the diluted Ho and Dy spin ice systems. X-ray absorption fine structure (EXAFS) spectra and x-ray diffraction show that the samples are structurally well ordered

[en] Measurements of electrical resistivity and AC magnetic susceptibility on the ferromagnetic oxide SrRuO₃ under hydrostatic pressure in the range 0≤qslantP≤qslant6.1GPa yield the pressure derivative of the Curie temperature ∂T_c/∂P=-5.7±0.2K/GPa where T_c(P=0) similar eq165K. This result is in qualitative agreement with the predictions of the Wohlfarth model. Our pressure results and the DC magnetization studies herein suggest the classification of this material as a moderately weak itinerant ferromagnet. ((orig.))