1,035 research outputs found
Magnetocaloric effect in the intermetallic compound DyNi
Magnetic and heat capacity measurements have been carried out on the
polycrystalline sample of DyNi which crystallizes in the orthorhombic FeB
structure (space group Pnma). This compound is ferromagnetic with a Curie
temperature of 59 K. Magnetization-field isotherms at low temperatures shows a
step-like behavior characteristic of metamagnetic transitions. The
magnetocaloric effect has been measured both in terms of isothermal magnetic
entropy change and adiabatic temperature change for various applied magnetic
fields. The maximum values of the entropy change and the temperature change are
found to be 19 Jkg-1K-1 and 4.5 K, respectively, for a field of 60 kOe. The
large magnetocaloric effect is attributed to the field-induced spin-flop
metamagnetism occurring in this compound, which has a noncollinear magnetic
structure at low fields.Comment: 11 page
Magnetic ordering of Mn sublattice, dense Kondo lattice behavior of Ce in (RPd3)8Mn (R = La, Ce)
We have synthesized two new interstitial compounds (RPd3)8Mn (R = La and Ce).
The Mn ions present in "dilute" concentration of just 3 molar percent form a
sublattice with an unusually large Mn-Mn near neighbor distance of ~ 85 nm.
While the existence of (RPd3)8M (where M is a p-block element) is already
documented in the literature, the present work reports for the first time the
formation of this phase with M being a 3d element. In (LaPd3)8Mn, the Mn
sub-lattice orders antiferromagnetically as inferred from the peaks in
low-field magnetization at 48 K and 23 K. The latter peak progressively shifts
towards lower temperatures in increasing magnetic field and disappears below
1.8 K in a field of ~ 8 kOe. On the other hand in (CePd3)8Mn the Mn sublattice
undergoes a ferromagnetic transition around 35 K. The Ce ions form a dense
Kondo-lattice and are in a paramagnetic state at least down to 1.5 K. A
strongly correlated electronic ground state arising from Kondo effect is
inferred from the large extrapolated value of C/T = 275 mJ/Ce-mol K^2 at T = 0
K. In contrast, the interstitial alloys RPd3Mnx (x = 0.03 and 0.06), also
synthesized for the first time, have a spin glass ground state due to the
random distribution of the Mn ions over the available "1b" sites in the parent
RPd3 crystal lattice.Comment: 18 figures and 20 pages of text documen
Magnetization studies on superconducting MgB - lower and upper critical fields and critical current density
Magnetization studies have been carried out on superconducting MgB
(T=37K) in the temperature range of 2-50K and in magnetic field up to 5
Tesla. From these measurements, values of the lower critical field H(0),
upper critical field H(0) at zero K are estimated to be ~300 Oe and ~12.5
Tesla, respectively, which yield a value of ~26 for the Ginzburg-Landau
parameter, k. Magnetization hysteresis loops have been obtained at various
temperatures from which the magnetization critical current density is estimated
using Bean's critical state model.Comment: 7 pages, 6 figures, to be publihed in Solid State Communications
(2001) [in press
Ferromagnetism in the Strong Hybridization Regime of the Periodic Anderson Model
We determine exactly the ground state of the one-dimensional periodic
Anderson model (PAM) in the strong hybridization regime. In this regime, the
low energy sector of the PAM maps into an effective Hamiltonian that has a
ferromagnetic ground state for any electron density between half and three
quarters filling. This rigorous result proves the existence of a new magnetic
state that was excluded in the previous analysis of the mixed valence systems.Comment: Accepted in Phys. Rev.
Anomalous NMR Magnetic Shifts in CeCoIn_5
We report ^{115}In and ^{59}Co Nuclear Magnetic Resonance (NMR) measurements
in the heavy fermion superconductor CeCoIn_5 above and below T_c. The hyperfine
couplings of the In and Co are anisotropic and exhibit dramatic changes below
50K due to changes in the crystal field level populations of the Ce ions. Below
T_c the spin susceptibility is suppressed, indicating singlet pairing.Comment: 4 pages, 4 figure
Superconductivity in the SU(N) Anderson Lattice at U=\infty
We present a mean-field study of superconductivity in a generalized N-channel
cubic Anderson lattice at U=\infty taking into account the effect of a
nearest-neighbor attraction J. The condition U=\infty is implemented within the
slave-boson formalism considering the slave bosons to be condensed. We consider
the -level occupancy ranging from the mixed valence regime to the Kondo
limit and study the dependence of the critical temperature on the various model
parameters for each of three possible Cooper pairing symmetries (extended s,
d-wave and p-wave pairing) and find interesting crossovers. It is found that
the d- and p- wave order parameters have, in general, very similar critical
temperatures. The extended s-wave pairing seems to be relatively more stable
for electronic densities per channel close to one and for large values of the
superconducting interaction J.Comment: Seven Figures; one appendix. Accepted for publication in Phys. Rev.
Planar 17O NMR study of Pr_yY_{1-y}Ba_2Cu_3O_{6+x}
We report the planar ^{17}O NMR shift in Pr substituted YBa_{2}Cu_{3}O_{6+x},
which at x=1 exhibits a characteristic pseudogap temperature dependence,
confirming that Pr reduces the concentration of mobile holes in the CuO_{2}
planes. Our estimate of the rate of this counterdoping effect, obtained by
comparison with the shift in pure samples with reduced oxygen content, is found
insufficient to explain the observed reduction of T_c. From the temperature
dependent magnetic broadening of the ^{17}O NMR we conclude that the Pr moment
and the local magnetic defect induced in the CuO_2 planes produce a long range
spin polarization in the planes, which is likely associated with the extra
reduction of T_c. We find a qualitatively different behaviour in the oxygen
depleted Pr_yY_{1-y}Ba_2Cu_3O_{6.6}, i.e. the suppression of T is nearly
the same, but the magnetic broadening of the ^{17}O NMR appears weaker. This
difference may signal a weaker coupling of the Pr to the planes in the
underdoped compound, which might be linked with the larger Pr to CuO_2 plane
distance, and correspondingly weaker hybridization.Comment: 8 pages, 9 figures, accepted in Phys Rev
Integrated Genomic Analysis of Diverse Induced Pluripotent Stem Cells from the Progenitor Cell Biology Consor tium
The rigorous characterization of distinct induced pluripotent stem cells (iPSC) derived from multiple reprogramming technologies,
somatic sources, and donors is required to understand potential sources of variability and downstream potential. To achieve this goal,
the Progenitor Cell Biology Consortium performed comprehensive experimental and genomic analyses of 58 iPSC from ten laboratories
generated using a variety of reprogramming genes, vectors, and cells. Associated global molecular characterization studies identified functionally
informative correlations in gene expression, DNA methylation, and/or copy-number variation among key developmental and
oncogenic regulators as a result of donor, sex, line stability, reprogramming technology, and cell of origin. Furthermore, X-chromosome
inactivation in PSC produced highly correlated differences in teratoma-lineage staining and regulator expression upon differentiation.
All experimental results, and raw, processed, and metadata from these analyses, including powerful tools, are interactively accessible
from a new online portal at https://www.synapse.org to serve as a reusable resource for the stem cell community
Itinerant Ferromagnetism in the Periodic Anderson Model
We introduce a novel mechanism for itinerant ferromagnetism, based on a
simple two-band model. The model includes an uncorrelated and dispersive band
hybridized with a second band which is narrow and correlated. The simplest
Hamiltonian containing these ingredients is the Periodic Anderson Model (PAM).
Using quantum Monte Carlo and analytical methods, we show that the PAM and an
extension of it contain the new mechanism and exhibit a non-saturated
ferromagnetic ground state in the intermediate valence regime. We propose that
the mechanism, which does not assume an intra atomic Hund's coupling, is
present in both the iron group and in some f electron compounds like
Ce(Rh_{1-x} Ru_x)_3 B_2, La_x Ce_{1-x} Rh_3 B_2 and the uranium
monochalcogenides US, USe, and UTe
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