155 research outputs found
Flux creep in the quasi-1D superconducting carbide Sc3CoC4
The superconducting flux dynamic of the transition metal carbide Sc3CoC4 which exhibits a quasi-one-dimensional structure is studied. Besides zero-field-cooling (zfc), field-cooling (fc) and magnetization measurements, especially flux creep relaxation experiments are performed. The relaxation rates S = dM/dlnt are determined at selected temperatures below the transition temperature Tc in two magnetic fields of 50 Oe and 100 Oe just above Hc1. The resulting supercurrent dependence on the mean activation energy is analyzed according to the collective pinning theory which predicts U ∼ ((j/jc)-μ –1). The calculated μ-values differ in the high and low temperature region. The μ-values below about 2.5 K are ≈ 0.5 - 0.68 depending slightly on the applied magnetic field whereas at higher temperatures the μ-values are ≈ 0.22 - 0.34. These results might indicate a transition between different types of vortex pinning around 2.5 K changing from single vortex creep at higher temperatures to collective creep of vortex bundles at lower temperatures
Orbital Freezing in FeCr2S4 Studied by Dielectric Spectroscopy
Broadband dielectric spectroscopy has been performed on single-crystalline
FeCr2S4 revealing a transition into a low-temperature orbital glass phase and
on polycrystalline FeCr2S4 where long-range orbital order is established via a
cooperative Jahn-Teller transition. The freezing of the orbital moments is
revealed by a clear relaxational behavior of the dielectric permittivity, which
allows a unique characterization of the orbital glass transition. The orbital
relaxation dynamics continuously slows down over six decades in time, before at
the lowest temperatures the glass transition becomes suppressed by quantum
tunneling.Comment: 4 pages, 4 figure
1D to 3D Dimensional Crossover in the Superconducting Transition of the Quasi-One-Dimensional Carbide Superconductor Sc3CoC4
The transition metal carbide superconductor Sc3CoC4 may represent a new
benchmark system of quasi-1D superconducting behavior. We investigate the
superconducting transition of a high-quality single crystalline sample by
electrical transport experiments. Our data show that the superconductor goes
through a complex dimensional crossover below the onset Tc of 4.5 K. First, a
quasi-1D fluctuating superconducting state with finite resistance forms in the
CoC4 ribbons which are embedded in a Sc matrix in this material. At lower
temperature, the transversal Josephson or proximity coupling of neighboring
ribbons establishes a 3D bulk superconducting state. This dimensional crossover
is very similar to Tl2Mo6Se6, which for a long time has been regarded as the
most appropriate model system of a quasi-1D superconductor. Sc3CoC4 appears to
be even more in the 1D limit than Tl2Mo6Se6
Thermal and Vibrational Properties of Thermoelectric ZnSb - Exploring the Origin of Low Thermal Conductivity
The intermetallic compound ZnSb is an interesting thermoelectric material,
largely due to its low lattice thermal conductivity. The origin of the low
thermal conductivity has so far been speculative. Using multi-temperature
single crystal X-ray diffraction (9 - 400 K) and powder X-ray diffraction (300
- 725 K) measurements we characterized the volume expansion and the evolution
of structural properties with temperature and identify an increasingly
anharmonic behavior of the Zn atoms. From a combination of Raman spectroscopy
and first principles calculations of phonons we consolidate the presence of
low-energy optic modes with wavenumbers below 60 cm-1. Heat capacity
measurements between 2 and 400 K can be well described by a Debye-Einstein
model containing one Debye and two Einstein contributions with temperatures
{\Theta}D = 195K, {\Theta}E1 = 78 K and {\Theta}E2 = 277 K as well as a
significant contribution due to anharmonicity above 150 K. The presence of a
multitude of weakly dispersed low-energy optical modes (which couple with the
acoustic, heat carrying phonons) combined with anharmonic thermal behavior
provides an effective mechanism for low lattice thermal conductivity. The
peculiar vibrational properties of ZnSb are attributed to its chemical bonding
properties which are characterized by multicenter bonded structural entities.
We argue that the proposed mechanism to explain the low lattice thermal
conductivity of ZnSb might also control the thermoelectric properties of
electron poor semiconductors, such as Zn4Sb3, CdSb, Cd4Sb3, Cd13-xInyZn10, and
Zn5Sb4In2-x.Comment: 25 pages, 10 figures, supporting information attache
Low field extension for magnetometers (TinyBee) used for investigations on low-dimensional superconductors with Bc1 < 5G
In this article a simple and easy to install low magnetic field extension of
the SQUID magnetometer Quantum Design MPMS-7 is described. This has been
accomplished by complementing the MPMS-7 magnet control system with a
laboratory current supply for the low magnetic field region (B \leq 200G). This
hard- and software upgrade provides a significant gain in the magnetic field
accuracy up to an order of magnitude compared with the standard instrument's
setup and is improving the resolution to better than 0.01G below 40G. The field
control has been integrated into the Quantum Design MultiVu software for a
transparent and user-friendly operation of this extension. The improvements
achieved are especially useful, when low magnetic field strengths (B < 1G) are
required at high precision. The specific advantages of this application are
illustrated by sophisticated magnetic characterisation of lowdimensional
superconductors like Sc3CoC4 and SnSe2{Co({\eta}-C5H5)2}x.Comment: 16 pages, 7 figure
An organometallic chimie douce approach to new Re(x)W(1-x)O3 phases
Re(x)W(1-x)O3.H2O and Re(x)W(1-x)O3 phases are prepared by a new
organometallic chimie douce concept employing the organometallic precursor
methyltrioxorhenium.Comment: 3 pages, 6 figures, submitted to Chem. Com
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