518 research outputs found
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
Interpretation of experimental results on Kondo systems with crystal field
We present a simple approach to calculate the thermodynamic properties of
single Kondo impurities including orbital degeneracy and crystal field effects
(CFE) by extending a previous proposal by K. D. Schotte and U. Schotte [Physics
Lett. A 55, 38 (1975)]. Comparison with exact solutions for the specific heat
of a quartet ground state split into two doublets shows deviations below
in absence of CFE and a quantitative agreement for moderate or large CFE. As an
application, we fit the measured specific heat of the compounds CeCuGe,
CePdSi, CePdAl, CePt, YbPdSn and YbCoZn. The
agreement between theory and experiment is very good or excellent depending on
the compound, except at very low temperatures due to the presence of magnetic
correlations (not accounted in the model)
Thermodynamic analysis of the Quantum Critical behavior of Ce-lattice compounds
A systematic analysis of low temperature magnetic phase diagrams of Ce
compounds is performed in order to recognize the thermodynamic conditions to be
fulfilled by those systems to reach a quantum critical regime and,
alternatively, to identify other kinds of low temperature behaviors. Based on
specific heat () and entropy () results, three different types of
phase diagrams are recognized: i) with the entropy involved into the ordered
phase () decreasing proportionally to the ordering temperature
(), ii) those showing a transference of degrees of freedom from the
ordered phase to a non-magnetic component, with their jump
() vanishing at finite temperature, and iii) those ending in a
critical point at finite temperature because their do not decrease
with producing an entropy accumulation at low temperature.
Only those systems belonging to the first case, i.e. with as
, can be regarded as candidates for quantum critical behavior.
Their magnetic phase boundaries deviate from the classical negative curvature
below \,K, denouncing frequent misleading extrapolations down to
T=0. Different characteristic concentrations are recognized and analyzed for
Ce-ligand alloyed systems. Particularly, a pre-critical region is identified,
where the nature of the magnetic transition undergoes significant
modifications, with its discontinuity strongly
affected by magnetic field and showing an increasing remnant entropy at . Physical constraints arising from the third law at are discussed
and recognized from experimental results
Electron concentration effects on the Shastry-Sutherland phase stability in Ce_{2-x}Pd_{2+y}In_{1-z} solid solutions
The stability of a Shastry-Sutherland ShSu phase as a function of electron
concentration is investigated through the field dependence of thermal and
magnetic properties of the solid solution Ce_{2-x}Pd_{2+y}In_{1-z} in the
antiferromagnetic branch. In these alloys the electronic (holes) variation is
realized by increasing concentration. The AF transition T_M decreases from
3.5K to 2.8K as concentration increases from y=0.2 to y=0.4. By applying
magnetic field, the ShSu phase is suppressed once the field induced
ferromagnetic polarization takes over at a critical field B_{cr} which
increases with content. A detailed analysis around the critical point
reveals a structure in the maximum of the dM/dB derivative, which is related
with incipient steps in the magnetization M(B) as predicted by the theory for
the ShSu lattice. The crossing of M(B) isotherms, observed in ShSu prototype
compounds, is also analyzed. The effect of substitution by is
interpreted as an increase of the number of 'holes' in the conduction band and
results in a unique parameter able to describe the variation of the magnetic
properties along the studied range of concentration.Comment: 8 pages, 11 figure
Exchange Narrowing Effects in the EPR Linewidth of Gd Diluted in Ce Compounds
Anomalous thermal behavior on the EPR linewidths of Gd impurities diluted in
Ce compounds has been observed. In metals, the local magnetic moment EPR
linewidth, \Delta H, is expected to increase linearly with the temperature. In
contrast, in Ce_{x}La_{1-x}Os_{2} the Gd EPR spectra show a nonlinear increase.
In this work, the mechanisms that are responsible for the thermal behavior of
the EPR lines in Ce_{x}La_{1-x}Os_{2} are examined. We show that the exchange
interaction between the local magnetic moments and the conduction electrons are
responsible for the narrowing of the spectra at low temperatures. At high
temperatures, the contribution to the linewidth of the exchange interaction
between the local magnetic moments and the ions has an exponential
dependence on the excitation energy of the intermediate valent ions. A complete
fitting of the EPR spectra for powdered samples is obtained.Comment: 11 pages, 1 figur
Effects of the target on the performance of an ultra-low power eddy current displacement sensor for industrial applications
The demand for smart, low-power, and low-cost sensors is rapidly increasing with the proliferation of industry automation. In this context, an Ultra-Low Power Eddy Current Displacement Sensor (ULP-ECDS) targeting common industrial applications and designed to be embedded in wireless Industrial Internet of Things (IIoT) devices is presented. A complete characterization of the realized ULP-ECDS operating with different metallic targets was carried out. The choice of the considered targets in terms of material and thickness was inspired by typical industrial scenarios. The experimental results show that the realized prototype works properly with extremely low supply voltages, allowing for obtaining an ultra-low power consumption, significantly lower than other state-of-the-art solutions. In particular, the proposed sensor reached the best resolution of 2 \ub5m in case of a carbon steel target when operated with a supply voltage of 200 mV and with a power consumption of 150 \ub5W. By accepting a resolution of 12 \ub5m, it is possible to further reduce the power consumption of the sensor to less than 10 \ub5W. The obtained results also demonstrate how the performances of the sensor are strongly dependent on both the target and the demodulation technique used to extract the displacement information. This allowed for defining some practical guidelines that can help the design of effective solutions considering application-specific constraints
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