470 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
Possible canted antiferromagnetism in UCuSn
We report on the new compound UCuSn which crystallizes in the
tetragonal structure \emph{I}4/\emph{mcm} with lattice parameters and . This compound is isotyp to the
ferromagnetic systems RECuSn (RE = Ce, Pr, Nd) with Curie
temperatures = 5.5 K, 10.5 K and 15 K, respectively.
UCuSn exhibits an uncommon magnetic behavior resulting in three
different electronic phase transitions. Below 105 K the sample undergoes a
valence transition accompanied by an entropy change of 0.5 Rln2. At 32 K a
small hump in the specific heat and a flattening out in the susceptibility
curve probably indicate the onset of helical spin order. To lower temperatures
a second transition to antiferromagnetic ordering occurs which develops a small
ferromagnetic contribution on lowering the temperature further. These results
are strongly hinting for canted antiferromagnetism in UCuSn.Comment: 2 pages, 3 figures, SCES0
The algebro-geometric initial value problem for the Ablowitz-Ladik hierarchy
We discuss the algebro-geometric initial value problem for the Ablowitz-Ladik
hierarchy with complex-valued initial data and prove unique solvability
globally in time for a set of initial (Dirichlet divisor) data of full measure.
To this effect we develop a new algorithm for constructing stationary
complex-valued algebro-geometric solutions of the Ablowitz-Ladik hierarchy,
which is of independent interest as it solves the inverse algebro-geometric
spectral problem for general (non-unitary) Ablowitz-Ladik Lax operators,
starting from a suitably chosen set of initial divisors of full measure.
Combined with an appropriate first-order system of differential equations with
respect to time (a substitute for the well-known Dubrovin-type equations), this
yields the construction of global algebro-geometric solutions of the
time-dependent Ablowitz-Ladik hierarchy.
The treatment of general (non-unitary) Lax operators associated with general
coefficients for the Ablowitz-Ladik hierarchy poses a variety of difficulties
that, to the best of our knowledge, are successfully overcome here for the
first time. Our approach is not confined to the Ablowitz-Ladik hierarchy but
applies generally to (1+1)-dimensional completely integrable soliton equations
of differential-difference type.Comment: 47 page
Antiferromagnetic behavior in CeCoGe
We investigate the novel intermetallic ternary compounds
\emph{R}CoGe with \emph{R} = La and Ce by means of -ray
diffraction, susceptibility and specific heat measurements. CeCoGe
crystallizes in the space group 4/ and is characterized by the
coexistence of two different magnetic sublattices. The Ce-based sublattice,
with an effective moment close to the expected value for a Ce-ion,
exhibits a magnetically ordered ground state with K. The
Co-based sublattice, however, exhibits magnetic moments due to itinerant 3
electrons. The magnetic specific heat contribution of the Ce-sublattice is
discussed in terms of a resonance-level model implying the interplay between an
antiferromagnetic phase transition and the Kondo-effect and an underlying
Schottky-anomaly indicating a crystal field level scheme splitting into three
twofold degenerated micro states ( K, K).Comment: 4 pages, 3 figures, conference SCES0
Crossover from Single-Ion to Coherent Non-Fermi Liquid Behavior in CeLaNiGe
We report specific heat and magneto-resistance studies on the compound
CeLaNiGe for various concentrations over the entire
stoichiometric range. Our data reveal single-ion scaling with Ce-concentration
between and 0.95. Furthermore, CeNiGe turns out to have
the largest ever recorded value of the electronic specific heat 5.5 J at K which was found in Cerium
f-electron lattice systems. In the doped samples increases
logarithmically in the temperature range between 3 K and 50 mK typical for
non-Fermi liquid (nFl) behavior, while exhibits a Kondo-like minimum
around 30 K, followed by a single-ion local nFl behavior. In contrast to this,
CeNiGe flattens out in below 300 mK and displays a
pronounced maximum in the resistivity curve at 1.5 K indicating a coherent
heavy fermion groundstate. These properties render the compound
CeLaNiGe a unique system on the borderline between
Fermi liquid and nFl physics.Comment: 2 pages, 3 figures, SCES0
Competing magnetic interactions in CeNi9-xCoxGe4
CeNi9Ge4 exhibits outstanding heavy fermion features with remarkable
non-Fermi- liquid behavior which is mainly driven by single-ion effects. The
substitution of Ni by Cu causes a reduction of both, the RKKY coupling and
Kondo interaction, coming along with a dramatic change of the crystal field
(CF) splitting. Thereby a quasi-quartet ground state observed in CeNi9Ge4
reduces to a two-fold degenerate one in CeNi8CuGe4. This leads to a
modiffcation of the effective spin degeneracy of the Kondo lattice ground state
and to the appearance of antiferromagnetic (AFM) order. To obtain a better
understanding of consequences resulting from a reduction of the effective spin
degeneracy, we stepwise replaced Ni by Co. Thereby an increase of the Kondo and
RKKY interactions through the reduction of the effective d-electron count is
expected. Accordingly, a paramagnetic Fermi liquid ground state should arise.
Our experimental studies, however, reveal AFM order already for small Co
concentrations, which becomes even more pronounced with increasing Co content
x. Thereby the modiffcation of the effective spin degeneracy seems to play a
crucial role in this system
Geodesic distance for right invariant Sobolev metrics of fractional order on the diffeomorphism group
We study Sobolev-type metrics of fractional order on the group
\Diff_c(M) of compactly supported diffeomorphisms of a manifold . We show
that for the important special case the geodesic distance on
\Diff_c(S^1) vanishes if and only if . For other manifolds we
obtain a partial characterization: the geodesic distance on \Diff_c(M)
vanishes for and for ,
with being a compact Riemannian manifold. On the other hand the geodesic
distance on \Diff_c(M) is positive for and
.
For we discuss the geodesic equations for these metrics. For
we obtain some well known PDEs of hydrodynamics: Burgers' equation for ,
the modified Constantin-Lax-Majda equation for and the
Camassa-Holm equation for .Comment: 16 pages. Final versio
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