30 research outputs found
Specific heat measurements and structural investigation of CeCu6 - xSnx compounds
International audienceThe evolution of the crystal structure and some magnetic properties of the heavy-fermion material CeCu6 - xSnx (x = 0, 0.25, 0.65, 0.75, 0.85 and 1.0) has been studied by powder neutron diffraction and by specific heat measurements. The substitution of Cu by Sn suppresses the temperature induced orthorhombic to monoclinic transition, known to occur in the pure CeCu6 phase. No structural phase transition has been observed in these samples as a function of x but the cell volume increases considerably in an anisotropic way. Sn occupies preferentially the special Cu crystallographic site which is next to each of the four Ce atoms in the unit cell. The transition to antiferromagnetic order, characterizing the samples with higher x, is sensitive to both x and magnetic field. The results are discussed in the context of the competition between Kondo and RKKY interactions in disordered or not heavy-fermion systems and reveal an interesting interplay between composition, structure and magnetism in CeCu6 - xSnx
A New Heavy-Fermion Superconductor CeIrIn5: Relative of the Cuprates?
CeIrIn5 is a member of a new family of heavy-fermion compounds and has a
Sommerfeld specific heat coefficient of 720 mJ/mol-K2. It exhibits a bulk,
thermodynamic transition to a superconducting state at Tc=0.40 K, below which
the specific heat decreases as T2 to a small residual T-linear value.
Surprisingly, the electrical resistivity drops below instrumental resolution at
a much higher temperature T0=1.2 K. These behaviors are highly reproducible and
field-dependent studies indicate that T0 and Tc arise from the same underlying
electronic structure. The layered crystal structure of CeIrIn5 suggests a
possible analogy to the cuprates in which spin/charge pair correlations develop
well above Tc
Magnetic structure of CeRhIn_5 as a function of pressure and temperature
We report magnetic neutron-diffraction and electrical resistivity studies on
single crystals of the heavy-fermion antiferromagnet CeRhIn at pressures
up to 2.3 GPa. These experiments show that the staggered moment of Ce and the
incommensurate magnetic structure change weakly with applied pressure up to
1.63 GPa, where resistivity, specific heat and NQR measurements confirm the
presence of bulk superconductivity. This work places new constraints on an
interpretation of the relationship between antiferromagnetism and
unconventional superconductivity in CeRhIn.Comment: 6 pages, 6 figures, submitted to 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
An Experimental and Theoretical Study of the Variation of 4f Hybridization Across the La1-xCexIn3 Series
Crystal structures of a series of La1-xCexIn3 (x = 0.02, 0.2, 0.5, or 0.8)
intermetallic compounds have been investigated by both neutron and X-ray
diffraction, and their physical properties have been characterized by magnetic
susceptibility and specific heat measurements. Our results emphasize atypical
atomic displacement parameters (ADP) for the In and the rare-earth sites.
Depending on the x value, the In ADP presents either an "ellipsoidal"
elongation (La-rich compounds) or a "butterfly-like" distortion (Ce-rich
compounds). These deformations have been understood by theoretical techniques
based on the band theory and are the result of hybridization between conduction
electrons and 4f-electrons.Comment: 7 pages, 8 figure
Magnetic Structure of Heavy Fermion Ce2RhIn8
Magnetic structure of the heavy fermion antiferromagnet Ce2RhIn8 is
determined using neutron diffraction.Comment: 4 pages, 3 figures, 1 tabl
Coexistence of magnetism and superconductivity in CeRh1-xIrxIn5
We report a thermodynamic and transport study of the phase diagram of
CeRh1-xIrxIn5. Superconductivity is observed over a broad range of doping, 0.3
< x < 1, including a substantial range of concentration (0.3 < x <0.6) over
which it coexists with magnetic order (which is observed for 0 < x < 0.6). The
anomalous transition to zero resistance that is observed in CeIrIn5 is robust
against Rh substitution. In fact, the observed bulk Tc in CeRh0.5Ir0.5In5 is
more than double that of CeIrIn5, whereas the zero-resistance transition
temperature is relatively unchanged for 0.5 < x < 1
Magnetic field dependence of low temperature specific heat of spinel oxide superconductor LiTi_2O_4
Magnetic field dependence of low temperature specific heat of spinel oxide
superconductor LiTi_2O_4 has been elaborately investigated. In the normal
state, the obtained electronic coefficient of specific heat gamma_n = 19.15
mJ/mol K2, the Debye temperature is 657 K and some other parameters are
compared with those reported earlier. The superconducting transition at Tc ~
11.4 K is very sharp (DeltaTc ~ 0.3 K) and the estimated delataC/gamma_nTc is ~
1.78. In the superconducting state, the best fit of data leads to the
electronic specific heat C_es/Gamma_nTc = 9.87 exp (-1.58 Tc/T) without field
and gamma(H) ~ H^0.95 with fields. In addition, Hc2(0) ~ 11.7 T, Hc(0) ~ 0.32
T, xi_GL(0) ~ 5.5 nm, lambda_GL(0) ~ 160 nm, and Hc1(0) ~ 26 mT are estimated
from Werthamer-Helfand-Hohenberg (WHH) theory or other relevant relations. All
results from the present study indicate that LiTi2O4 can be well described by a
typical type-II, BCS-like, moderate coupling, and fully gapped superconductor
in the dirty limit. It is further suggested that LiTi2O4 is a moderately
electron-electron correlated system.Comment: 6 pages, 2 tables, 6 figures; Physical Review B, in pres
Heat capacity studies of Ce and Rh site substitution in the heavy fermion antiferromagnet CeRhIn_5;: Short-range magnetic interactions and non-Fermi-liquid behavior
In heavy fermion materials superconductivity tends to appear when long range
magnetic order is suppressed by chemical doping or applying pressure. Here we
report heat capacity measurements on diluted alloyes of the heavy fermion
superconductor CeRhIn_5;. Heat capacity measurements have been performed on
CeRh_{1-y}Ir_{y}In_5; (y <= 0.10) and Ce_{1-x}La_{x}Rh_{1-y}Ir_{y}In_5; (x <=
0.50) in applied fields up to 90 kOe to study the affect of doping and magnetic
field on the magnetic ground state. The magnetic phase diagram of
CeRh_{0.9}Ir_{0.1}In_5; is consistent with the magnetic structure of CeRhIn_5;
being unchanged by Ir doping. Doping of Ir in small concentrations is shown to
slightly increase the antiferromagnetic transition temperature T_{N} (T_{N}=3.8
K in the undoped sample). La doping which causes disorder on the Ce sublattice
is shown to lower T_{N} with no long range order observed above 0.34 K for
Ce_{0.50}La_{0.50}RhIn_5;. Measurements on Ce_{0.50}La_{0.50}RhIn_5; show a
coexistence of short range magnetic order and non-Fermi-liquid behavior. This
dual nature of the Ce 4f-electrons is very similar to the observed results on
CeRhIn_5; when long range magnetic order is suppressed at high pressure.Comment: 8 pages, 9 figure