17 research outputs found
Experimental evidence of s-wave superconductivity in bulk CaC
The temperature dependence of the in-plane magnetic penetration depth,
, has been measured in a c-axis oriented polycrystalline
CaC bulk sample using a high-resolution mutual inductance technique. A
clear exponential behavior of has been observed at low
temperatures, strongly suggesting isotropic s-wave pairing. Data fit using the
standard BCS theory yields Angstroem and
meV. The ratio
gives indication for a conventional weakly coupled superconductor.Comment: To appear in Phys. Rev. Let
Superconductivity of bulk CaC6
We have obtained bulk samples of the graphite intercalation compound, CaC6,
by a novel method of synthesis from highly oriented pyrolytic graphite. The
crystal structure has been completely determined showing that it is the only
member of the MC6, metal-graphite compounds, which has rhombohedral symmetry.
We have clearly shown the occurrence of superconductivity in the bulk sample at
11.5K, using magnetization measurements.Comment: 8 pages of text + 4 figures = 12 page
Short-range magnetic order, irreversibility and giant magnetoresistance near the triple points in the (
We have studied pseudo-layered ZrMn6Sn6-xGax intermetallics (0.55 †x †0.81) using magnetic, magnetoresistivity and powder neutron diffraction measurements. All the alloys studied have magnetic ordering temperatures in the 450-490 K temperature range. They present complex temperature-dependent partially disordered magnetic structures whose ferromagnetic component develops upon increasing the Ga content. ZrMn6Sn6-xGax alloys with x †0.69 are essentially collinear antiferromagnets at high-temperature and adopt antifan-like arrangements at low temperature. For x ℠0.75, the alloys order ferromagnetically and evolve to a fan-like structure upon cooling. The intermediate compositions (x = 0.71 and 0.73) present a canted fan-like order at high temperature and another kind of antifan-like arrangement at low temperature. The degree of short-range order tends to increase upon approaching the intermediate
compositions. The (x, T) phase diagram contains two triple points (x ~ 0.70; T ~ 460Â K and x ~ 0.74; T ~ 455Â K), where the paramagnetic, an incommensurate and a commensurate phases meet, which possess some of the features of Lifshitz point. Irreversibilities manifest in the low-temperature magnetization curves at the antifan-fan or fan-ferromagnetic boundaries as well as inside the fan region. Giant magnetoresistance is observed, even above room temperature
Magnetic properties and
We have synthesized LiMn6Sn6, the first RMn6Sn6
compound involving an alkali metal as R element. It crystallizes in
the hexagonal (P6/mmm) HfFe6Ge6-type structure. From magnetic
measurements and powder neutron diffraction experiments it is found
that LiMn6Sn6 magnetically orders at TC = 380 K
in a simple easy-plane ferromagnetic structure (mMn = 2.58 ÎŒB
at 2 K). The 119Sn Mössbauer spectrum recorded at 5 K indicates
that the tin nuclei experience huge hyperfine fields (as large as
35 T). Electronic structure calculations are used to gain information
about the microscopic origin of both the hyperfine field and electric
field gradient at the Sn nuclei. The former arises due to spin-dependent
hybridization between the 5s states of Sn and the 3d states
of Mn. The latter comes from the 5p charge density close to the
nucleus, whose anisotropy is mainly produced through directional interactions
with the 3d states of the first Mn neighbors. Comparison between
experimental quadrupole splittings and theoretical electric field
gradients allows us to propose a value of for the quadrupole moment of the first excited state (I= 3/2) of the 119Sn nucleus
Short-range magnetic order, irreversibility and giant magnetoresistance near the triple points in the (x, T) magnetic phase diagram of ZrMn 6Sn 6-x Ga x
Direct Revealing of the Occupation Sites of Heavy Alkali Metal Atoms in Single-Walled Carbon Nanotube Intercalation Compounds
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