1,343 research outputs found
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
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
Unusual Non-Fermi Liquid Behavior of CeLaNiGe Analyzed in a Single Impurity Anderson Model with Crystal Field Effects
CeNiGe exhibits unusual non-Fermi liquid behavior with the largest
ever recorded value of the electronic specific heat
JKmol without showing any evidence of magnetic order. Specific
heat measurements show that the logarithmic increase of the Sommerfeld
coefficient flattens off below 200 mK. In marked contrast, the local
susceptibility levels off well above 200 mK and already becomes
constant below 1 K. Furthermore, the entropy reaches 2ln2 below 20 K
corresponding to a four level system. An analysis of and was
performed in terms of an single impurity Anderson model with
additional crystal electric field (CEF) splitting. Numerical renormalization
group calculations point to a possible consistent description of the different
low temperature scales in and stemming from the
interplay of Kondo effect and crystal field splitting.Comment: 2 pages, 2 figure
Evolution of Quantum Criticality in CeNi_{9-x}Cu_xGe_4
Crystal structure, specific heat, thermal expansion, magnetic susceptibility
and electrical resistivity studies of the heavy fermion system
CeNi_{9-x}Cu_xGe_4 (0 <= x <= 1) reveal a continuous tuning of the ground state
by Ni/Cu substitution from an effectively fourfold degenerate non-magnetic
Kondo ground state of CeNi_9Ge_4 (with pronounced non-Fermi-liquid features)
towards a magnetically ordered, effectively twofold degenerate ground state in
CeNi_8CuGe_4 with T_N = 175 +- 5 mK. Quantum critical behavior, C/T ~ \chi ~
-ln(T), is observed for x about 0.4. Hitherto, CeNi_{9-x}Cu_xGe_4 represents
the first system where a substitution-driven quantum phase transition is
connected not only with changes of the relative strength of Kondo effect and
RKKY interaction, but also with a reduction of the effective crystal field
ground state degeneracy.Comment: 15 pages, 9 figure
Unusual Single-Ion Non-Fermi Liquid Behavior in Ce_(1-x)La_xNi_9Ge_4
We report on specific heat, magnetic susceptibility and resistivity
measurements on the compound Ce_(1-x)La_xNi_9Ge_4 for various concentrations
ranging from the stoichiometric system with x=0 to the dilute limit x=0.95. Our
data reveal single-ion scaling with the Ce-concentration and the largest ever
recorded value of the electronic specific heat c/T approximately 5.5 J
K^(-2)mol^(-1) at T=0.08K for the stoichiometric compound x=0 without any trace
of magnetic order. While in the doped samples c/T increases logarithmically
below 3K down to 50mK, their magnetic susceptibility behaves Fermi liquid like
below 1K. These properties make the compound Ce_(1-x)La_xNi_9Ge_4 a unique
system on the borderline between Fermi liquid and non-Fermi liquid physics.Comment: 4 pages, 5 figures; v2 contains additional resisitivity measurements;
final version to appear in Phys. Rev. Let
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
Spin and orbital frustration in MnSc_2S_4 and FeSc_2S_4
Crystal structure, magnetic susceptibility, and specific heat were measured
in the normal cubic spinel compounds MnSc_2S_4 and FeSc_2S_4. Down to the
lowest temperatures, both compounds remain cubic and reveal strong magnetic
frustration. Specifically the Fe compound is characterized by a Curie-Weiss
temperature \Theta_{CW}= -45 K and does not show any indications of order down
to 50 mK. In addition, the Jahn-Teller ion Fe^{2+} is orbitally frustrated.
Hence, FeSc_2S_4 belongs to the rare class of spin-orbital liquids. MnSc_2S_4
is a spin liquid for temperatures T > T_N \approx 2 K.Comment: 4 pages, to be published in Physical Review Letter
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