6,021 research outputs found
Magnetic, thermal and transport properties of Cd doped CeIn
We have investigated the effect of Cd substitution on the archetypal heavy
fermion antiferromagnet CeIn via magnetic susceptibility, specific heat and
resistivity measurements. The suppression of the Neel temperature, T,
with Cd doping is more pronounced than with Sn. Nevertheless, a doping induced
quantum critical point does not appear to be achievable in this system. The
magnetic entropy at and the temperature of the maximum in resistivity are
also systematically suppressed with Cd, while the effective moment and the
Curie-Weiss temperature in the paramagnetic state are not affected. These
results suggest that Cd locally disrupts the AFM order on its neighboring Ce
moments, without affecting the valence of Ce. Moreover, the temperature
dependence of the specific heat below is not consistent with 3D magnons
in pure as well as in Cd-doped CeIn, a point that has been missed in
previous investigations of CeIn and that has bearing on the type of quantum
criticality in this system
Purging of a multilayer insulation with dacron tuft spacer by gas diffusion
The time and purge gas usage required to purge a multilayer insulation (MLI) panel with gaseous helium by means of gas diffusion to obtain a condensable gas (nitrogen) concentration of less than 1 percent within the panel are stipulated. Two different, flat, rectangular MLI panels, one incorporating a butt joint, were constructed of of 11 double-aluminized Mylar (DAM) radiation shields separated by Dacron tuft spacers. The DAM/Dacron tuft concept is known commercially as Superfloc. The nitrogen gas concentration as a function of time within the MLI panel could be adequately predicted by using a simple, one dimensional gas diffusion model in which the boundary conditions at the edge of the MLI panel were time dependent. The time and purge gas usage required to achieve 1 percent nitrogen gas concentration within the MLI panel varied from 208 to 86 minutes and 34.1 to 56.5 MLI panel purge volumes, respectively, for gaseous helium purge rates from 10 to 40 MLI panel volumes per hour
A New Heavy-Fermion Superconductor CeIrIn5: Relative of the Cuprates?
CeIrIn5 is a member of a new family of heavy-fermion compounds and has a
Sommerfeld specific heat coefficient of 720 mJ/mol-K2. It exhibits a bulk,
thermodynamic transition to a superconducting state at Tc=0.40 K, below which
the specific heat decreases as T2 to a small residual T-linear value.
Surprisingly, the electrical resistivity drops below instrumental resolution at
a much higher temperature T0=1.2 K. These behaviors are highly reproducible and
field-dependent studies indicate that T0 and Tc arise from the same underlying
electronic structure. The layered crystal structure of CeIrIn5 suggests a
possible analogy to the cuprates in which spin/charge pair correlations develop
well above Tc
The Fermi surface of CeCoIn5: dHvA
Measurements of the de Haas - van Alphen effect in the normal state of the
heavy Fermion superconductor CeCoIn5 have been carried out using a torque
cantilever at temperatures ranging from 20 to 500 mK and in fields up to 18
tesla. Angular dependent measurements of the extremal Fermi surface areas
reveal a more extreme two dimensional sheet than is found in either CeRhIn5 or
CeIrIn5. The effective masses of the measured frequencies range from 9 to 20
m*/m0.Comment: 4 pages, 2 figures, submitted to PRB Rapid
Saturation of electrical resistivity in metals at large temperatures
We present a microscopic model for systems showing resistivity saturation. An
essentially exact quantum Monte-Carlo calculation demonstrates that the model
describes saturation. We give a simple explanation for saturation, using charge
conservation and considering the limit where thermally excited phonons have
destroyed the periodicity. Crucial model features are phonons coupling to the
hopping matrix elements and a unit cell with several atoms. We demonstrate the
difference to a model of alkali-doped C60 with coupling to the level positions,
for which there is no saturation.Comment: 4 page, RevTeX, 3 eps figures, additional material available at
http://www.mpi-stuttgart.mpg.de/andersen/fullerene
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