1,121 research outputs found
Phase diagram of CeVSb3 under pressure and its dependence on pressure conditions
We present temperature dependent resistivity and ac-calorimetry measurements
of CeVSb3 under pressure up to 8 GPa in a Bridgman anvil cell modified to use a
liquid medium and in a diamond anvil cell using argon as a pressure medium,
respectively. We observe an initial increase of the ferromagnetic transition
temperature Tc with pressures up to 4.5 GPa, followed by decrease of Tc on
further increase of pressure and finally its disappearance, in agreement with
the Doniach model. We infer a ferromagnetic quantum critical point around 7 GPa
under hydrostatic pressure conditions from the extrapolation to 0 K of Tc and
the maximum of the A coefficient from low temperature fits of the resistivity
\rho (T)=\rho_{0}+AT^{n}. No superconductivity under pressure was observed down
to 0.35 K for this compound. In addition, differences in the Tc(P) behavior
when a slight uniaxial component is present are noticed and discussed and
correlated to choice of pressure medium
Two-Dimensional Nature of Four-Layer Superconductors by Inequivalent Hole Distribution
The magnetization of the four-layer superconductor
CuBa_{2}Ca_{3}Cu_4O_{12-\delta} with T_c\simeq117 K is presented. The
high-field magnetization around T_c(H) follows the exact two-dimensional
scaling function given by Te\v{s}anovi\'{c} and Andreev. This feature is
contrary to the inference that the interlayer coupling becomes strong if the
number of CuO_2 planes in a unit cell increases. Also, the fluctuation-induced
susceptibility in the low-field region was analyzed by using the modified
Lawrence-Doniach model. The effective number of independently fluctuating CuO_2
layers per unit cell, g_{\rm eff}, turned out to be \simeq 2 rather than 4,
which indicated that two among the four CuO_2 layers were in states far from
their optimal doping levels. This result could explain why
CuBa_{2}Ca_{3}Cu_4O_{12-\delta} shows two-dimensional behavior.Comment: 5 pages and 4 figure
Remarkably robust and correlated coherence and antiferromagnetism in (CeLa)CuGe
We present magnetic susceptibility, resistivity, specific heat, and
thermoelectric power measurements on (CeLa)CuGe single
crystals (0 1). With La substitution, the antiferromagnetic
temperature is suppressed in an almost linear fashion and moves below
0.36 K, the base temperature of our measurements for 0.8. Surprisingly, in
addition to robust antiferromagnetism, the system also shows low temperature
coherent scattering below up to 0.9 of La, indicating a small
percolation limit 9 of Ce that separates a coherent regime from a
single-ion Kondo impurity regime. as a function of magnetic field was
found to have different behavior for 0.9. Remarkably,
at = 0 was found to be linearly proportional to . The
jump in the magnetic specific heat at as a function of
for (CeLa)CuGe follows the theoretical prediction
based on the molecular field calculation for the = 1/2 resonant level
model
Crystal growth and annealing study of fragile, non-bulk superconductivity in YFeGe
We investigated the occurrence and nature of superconductivity in single
crystals of YFeGe grown out of Sn flux by employing x-ray diffraction,
electrical resistivity, and specific heat measurements. We found that the
residual resistivity ratio (RRR) of single crystals can be greatly improved,
reaching as high as 60, by decanting the crystals from the molten Sn at
350C and/or by annealing at temperatures between 550C and
600C. We found that samples with RRR 34 showed resistive
signatures of superconductivity with the onset of the superconducting
transition K. RRR values vary between 35 and 65 with, on
average, no systematic change in value, indicating that systematic
changes in RRR do not lead to comparable changes in . Specific heat
measurements on samples that showed clear resistive signatures of a
superconducting transition did not show any signature of a superconducting
phase transition, which suggests that the superconductivity observed in this
compound is either some sort of filamentary, strain stabilized
superconductivity associated with small amounts of stressed YFeGe
(perhaps at twin boundaries or dislocations) or is a second crystallographic
phase present at levels below detection capability of conventional powder x-ray
techniques.Comment: 8 pages, 11 figure
Thermoelectric power of Ba(Fe1-xRux)2As2 and Ba(Fe1-xCox)2As2: possible changes of Fermi surface with and without changes in electron count
Temperature-dependent, in-plane, thermoelectric power (TEP) data are
presented for Ba(Fe1-xRux)2As2 (0 < x < 0.36) single crystals. The previously
outlined x - T phase diagram for this system is confirmed. The analysis of TEP
evolution with Ru-doping suggests significant changes in the electronic
structure, correlations and/or scattering occurring near ~7% and ~30% of
Ru-doping levels. These results are compared with an extended set of TEP data
for the electron-doped Ba(Fe1-xCox)2As2 series
Neutron scattering and scaling behavior in URu2Zn20 and YbFe2Zn20
The dynamic susceptibility chi"(deltaE), measured by inelastic neutron
scattering measurements, shows a broad peak centered at Emax = 16.5 meV for the
cubic actinide compound URu2Zn20 and 7 meV at the (1/2, 1/2, 1/2) zone boundary
for the rare earth counterpart compound YbFe2Zn20. For URu2Zn20, the low
temperature susceptibility and magnetic specific heat coefficient gamma =
Cmag/T take the values chi = 0.011 emu/mole and gamma = 190 mJ/mole-K2 at T = 2
K. These values are roughly three times smaller, and Emax is three times
larger, than recently reported for the related compound UCo2Zn20, so that chi
and gamma scale inversely with the characteristic energy for spin fluctuations,
Tsf = Emax/kB. While chi(T), Cmag(T), and Emax of the 4f compound YbFe2Zn20 are
very well described by the Kondo impurity model, we show that the model works
poorly for URu2Zn20 and UCo2Zn20, suggesting that the scaling behavior of the
actinide compounds arises from spin fluctuations of itinerant 5f electrons.Comment: 7 pages, 5 figure
Tuning low-temperature physical properties of CeNiGe3 by magnetic field
We have studied the thermal, magnetic, and electrical properties of the ternary intermetallic system CeNiGe3 by means of specific heat, magnetization, and resistivity measurements. The specific heat data, together with the anisotropic magnetic susceptibility, was analyzed on the basis of the point charge model of crystalline electric field. The J=5/2 multiplet of the Ce3+ is split by the crystalline electric field into three Kramers doublets, where the second and third doublets are separated from the first (ground state) doublet by Δ1∼100 K and Δ2∼170 K, respectively. In zero field CeNiGe3 exhibits an antiferromangeic order below TN=5.0 K. For H∥a two metamagnetic transitions are clearly evidenced between 2–4 K from the magnetization isotherm and extended down to 0.4 K from the magnetoresistance measurements. For H∥a, TN shifts to lower temperature as magnetic field increases, and ultimately disappears at Hc∼32.5 kOe. For H\u3eHc, the electrical resistivity shows the quadratic temperature dependence (Δρ=AT2). For H⪢Hc, an unconventional Tn dependence of Δρ with n\u3e2 emerges, the exponent n becomes larger as magnetic field increases. Although the antiferromagnetic phase transition temperature in CeNiGe3 can be continuously suppressed to zero, it provides an example of field tuning that does not match current simple models of quantum criticality
Thermoelectric power of the YbT2Zn20 (T = Fe, Ru, Os, Ir, Rh, and Co) heavy fermions
The thermoelectric power, S(T), of the heavy fermions YbT2Zn20 (T = Fe, Ru, Os, Ir, Rh, and Co) has been measured to shed further light on their strong electronic correlations. A large, negative, local minimum in S(T) with approximately −70 μV/K is found for all compounds. From the observed local minimum, the energy scales associated with both the Kondo temperature and the crystalline electric field splitting are deduced and compared to previous specific heat measurements. At low temperatures, a highly enhanced S(T)/T value is observed for all members, although S(T) does show a deviation from a purely linear temperature dependence, S(T) = αT, for T ≠ Fe members. In the zero-temperature limit, estimated by a simple linear extrapolation, the enhanced S(T)/T value strongly correlates with the electronic specific heat coefficient, C(T)/T
The Infrared Einstein Ring in the Gravitational Lens MG1131+0456 and the Death of the Dusty Lens Hypothesis
We have obtained and modeled new NICMOS images of the lens system
MG1131+0456, which show that its lens galaxy is an H=18.6 mag, transparent,
early-type galaxy at a redshift of about z_l = 0.85; it has a major axis
effective radius R_e=0.68+/-0.05 arcsec, projected axis ratio b/a=0.77+/-0.02,
and major axis PA=60+/-2 degrees. The lens is the brightest member of a group
of seven galaxies with similar R-I and I-H colors, and the two closest group
members produce sufficient tidal perturbations to explain the ring morphology.
The host galaxy of the MG1131+0456 source is a z_s > 2 ERO (``extremely red
object'') which is lensed into optical and infrared rings of dramatically
different morphologies. These differences imply a strongly wavelength-dependent
source morphology that could be explained by embedding the host in a larger,
dusty disk. At 1.6 micron (H), the ring is spectacularly luminous, with a total
observed flux of H=17.4 mag and a de-magnified flux of 19.3 mag, corresponding
to a 1-2L_* galaxy at the probable source redshift of z_s > 2. Thus, it is
primarily the stellar emission of the radio source host galaxy that produces
the overall colors of two of the reddest radio lenses, MG1131+0456 and
B~1938+666, aided by the suppression of optical AGN emission by dust in the
source galaxy. The dusty lens hypothesis -- that many massive early-type
galaxies with 0.2 < z_l < 1.0 have large, uniform dust opacities -- is ruled
out.Comment: 27 pages, 8 COLOR figures, submitted to ApJ. Black and white version
available at http://cfa-www.harvard.edu/castle
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