17,938 research outputs found
Nonlinear viscoelasticity of metastable complex fluids
Many metastable complex fluids such as colloidal glasses and gels show
distinct nonlinear viscoelasticity with increasing oscillatory-strain
amplitude; the storage modulus decreases monotonically as the strain amplitude
increases whereas the loss modulus has a distinct peak before it decreases at
larger strains. We present a qualitative argument to explain this ubiquitous
behavior and use mode coupling theory (MCT) to confirm it. We compare
theoretical predictions to the measured nonlinear viscoelasticity in a dense
hard sphere colloidal suspensions; reasonable agreement is obtained. The
argument given here can be used to obtain new information about linear
viscoelasticity of metastable complex fluids from nonlinear strain
measurements.Comment: 7 pages, 3 figures, accepted for publication in Europhys. Let
Anisotropic magnetic behavior of GdBa_2Cu_3O_{6+y} single crystals
Magnetic properties of high-quality Al-free nonsuperconducting
GdBa_2Cu_3O_{6+y} single crystals grown by flux method have been studied. The
magnetic anisotropy below the N\'eel temperature T_N~2.3K corresponds to the
direction of Gd^{3+} magnetic moments along the tetragonal c-axis. At T < T_N
clear indications of spin-flop transitions for H||c have been observed on
magnetization curves at H_{sf}~10kOe. Magnetic phase diagrams have been
obtained for H||c as well as for H||ab. A pronounced anisotropy in the magnetic
susceptibility (unexpected for Gd-based compounds) has been found above T_N.Comment: 2 pages, 3 figures; LT23 (Aug. 2002; Hiroshima), accepted to Physica
The role of carbon for superconductivity in MgCNi from specific heat
The influence of carbon deficiency on superconductivity of MgCNi is
investigated by specific heat measurements in the normal and superconducting
state. In order to perform a detailed analysis of the normal state specific
heat, a computer code is developed which allows for an instantaneous estimate
of the main features of the lattice dynamics. By analyzing the evolution of the
lattice vibrations within the series and simultaneously considering the visible
mass enhancement, the loss in the electron-phonon coupling can be attributed to
significant changes of the prominent Ni vibrations. The present data well
supports the recently established picture of strong electron-phonon coupling
and ferromagnetic spin fluctuations in this compound.Comment: 4 pages, latex, corrections to the text, one reference added, one
figure correcte
Magnetic properties of Gd_{1-x}Pr_xBa_2Cu_3O_{7-y} single crystals
Magnetic properties were studied for the high quality Al-free orthorhombic
Gd_{1-x}Pr_xBa_2Cu_3O_{7-y} single crystals (0<=x<=1.0) grown by the flux
method. An indication on the interaction between the Pr and Cu(2) magnetic
sublattices was found for Pr123. Different signs of magnetic anisotropy were
established for the Pr and Gd ions at low temperatures. It was also shown that
superconductivity reported by Zou et al. [Phys. Rev. Lett. 80 (1998) 1074] for
Pr123 single crystals grown by TSZF method seems to be connected with partial
substitution of Ba for the Pr-sites.Comment: 2 pages (LaTeX2e), 4 EPS figures, phbauth style file included. LT22
conference paper accepted to Physica
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