391 research outputs found
Intermediate valence behavior in CeCo9Si4
The novel ternary compound CeCoSi has been studied by means of
specific heat, magnetisation, and transport measurements. Single crystal X-ray
Rietveld refinements reveal a fully ordered distribution of Ce, Co and Si atoms
with the tetragonal space group I4/mcm isostructural with other RCo9Si4. The
smaller lattice constants of CeCo9Si4 in comparison with the trend established
by other RCo9Si4 is indicative for intermediate valence of cerium. While
RCo9Si4 with R= Pr, .. Tb, and Y show ferromagnetism and LaCo9Si4 is nearly
ferromagnetic, CeCo9Si4 remains paramagnetic even in external fields as large
as 40 T, though its electronic specific heat coefficient (g~190 mJ/molK^2) is
of similar magnitude as that of metamagnetic LaCo9Si4 and weakly ferromagnetic
YCo9Si4.Comment: 2 pages, 3 figures, submitted to SCES 0
Superconductivity in novel Ge-based skutterudites: {Sr,Ba}Pt_4Ge_{12}
Combining experiments and ab initio models we report on
and as members of a novel class of superconducting
skutterudites, where Sr or Ba atoms stabilize a framework entirely formed by
Ge-atoms. Below K, and 5.10 K for and , respectively, electron-phonon coupled superconductivity
emerges, ascribed to intrinsic features of the Pt-Ge framework, where Ge-
states dominate the electronic structure at the Fermi energy.Comment: 4 pages, 4 figures, accepted for publication in PR
Heavy fermion superconductivity and magnetic order in non-centrosymmetric
is a novel heavy fermion superconductor, crystallising in the
structure as a tetragonally distorted low symmetry variant of the
structure type. exhibits antiferromagnetic order at
K and enters into a heavy fermion superconducting state at
K. Large values of T/K and T refer to heavy quasiparticles forming Cooper pairs. Hitherto, is the first heavy fermion superconductor without a center of
symmetry.Comment: 4 pages, 4 figure
Heavy Fermion Behavior, Crystalline Electric Field Effects, and Weak Ferromagnetism in SmOs_{4}Sb_{12}
The filled skutterudite compound SmOs_{4}Sb_{12} was prepared in single
crystal form and characterized. The SmOs_{4}Sb_{12} crystals have the
LaFe_{4}P_{12}-type structure with lattice parameter a = 9.3085 Angstroms.
Specific heat measurements indicate a large electronic specific heat
coefficient of ~880 mJ/mol K^{2}, from which an enhanced effective mass m^{*} ~
170 m_{e} is estimated. The specific heat data also suggest crystalline
electric field (CEF) splitting of the Sm^{3+} J = 5/2 multiplet into a
Gamma_{7} doublet ground state and a Gamma_{8} quartet excited state separated
by 37 K. Electrical resistivity rho(T) measurements reveal a decrease in rho(T)
below ~50 K that is consistent with CEF splitting of ~33 K between a Gamma_(7)
doublet ground state and Gamma_{8} quartet excited state. Specific heat and
magnetic susceptibility measurements display a possible weak ferromagnetic
transition at ~2.6 K, which could be an intrinsic property of SmOs_4Sb_{12} or
possibly due to an unknown impurity phase.Comment: 24 pages, 11 Postscript figures, to be published in Physical Review
A new polymorphic material? Structural degeneracy of ZrMn_2
Based on density functional calculations, we propose that ZrMn_2 is a
polymorphic material. We predict that at low temperatures the cubic C15, and
the hexagonal C14 and C36 structures of the Laves phase compound ZrMn_2 are
nearly equally stable within 0.3 kJmol^{-1} or 30 K. This degeneracy occurs
when the Mn atoms magnetize spontaneously in a ferromagnetic arrangement
forming the states of lowest energy. From the temperature dependent free
energies at T approx 160K we predict a transition from the most stable C15 to
the C14 structure, which is the experimentally observed structure at elevated
temperatures.Comment: 4 pages, 3 figure
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