694 research outputs found
Superconducting Properties of MgB2 Bulk Materials Prepared by High Pressure Sintering
High-density bulk materials of a newly discovered 40K intermetallic MgB2
superconductor were prepared by high pressure sintering. Superconducting
transition with the onset temperature of 39K was confirmed by both magnetic and
resistive measurements. Magnetization versus field (M-H) curve shows the
behavior of a typical Type II superconductor and the lower critical field
Hc1(0) estimated from M-H curve is 0.032T. The bulk sample shows good
connection between grains and critical current density Jc estimated from the
magnetization hysteresis using sample size was 2x104A/cm2 at 20K and 1T. Upper
critical field Hc2(0) determined by extrapolating the onset of resistive
transition and assuming a dirty limit is 18T.Comment: 3Pages PD
Suppression of Magnetic Order by Pressure in BaFe2As2
We performed the dc resistivity and the ZF 75As-NMR measurement of BaFe2As2
under high pressure. The T-P phase diagram of BaFe2As2 determined from
resistivity anomalies and the ZF 75As-NMR clearly revealed that the SDW anomaly
is quite robust against P.Comment: 2 pages, 2 figure
Microwave Penetration Depth and Quasiparticle Conductivity in PrFeAsO_1-y Single Crystals : Evidence for a Full-Gap Superconductor
In-plane microwave penetration depth and quaiparticle
conductivity at 28 GHz are measured in underdoped single crystals of the
Fe-based superconductor PrFeAsO ( K) by using a
sensitive superconducting cavity resonator. shows flat
dependence at low temperatures, which is incompatible with the presence of
nodes in the superconducting gap . The temperature dependence
of the superfluid density demonstrates that the gap is non-zero
() all over the Fermi surface. The microwave
conductivity below exhibits an enhancement larger than the coherence
peak, reminiscent of high- cuprate superconductors.Comment: 4 pages, 3 figures. Version accepted for publication in Phys. Rev.
Lett. For related results of hole-doped 122 system, see arXiv:0810.350
Uniform Mixing of High-Tc Superconductivity and Antiferromagnetism on a Single CuO2 Plane in Hg-based Five-layered Cuprate
We report a site selective Cu-NMR study on under-doped Hg-based five-layered
high- cuprate HgBa2Ca4Cu5Oy with a Tc=72 K. Antiferromagnetism (AF)
has been found to take place at TN=290 K, exhibiting a large antiferromagnetic
moment of 0.67-0.69uB at three inner planes (IP's). This value is comparable to
the values reported for non-doped cuprates, suggesting that the IP may be in a
nearly non-doped regime. Most surprisingly, the AF order is also detected with
M(OP)=0.1uB even at two outer planes (OP's) that are responsible for the onset
of superconductivity (SC). The high-Tc SC at Tc = 72 K can uniformly coexist on
a microscopic level with the AF at OP's. This is the first microscopic evidence
for the uniform mixed phase of AF and SC on a single CuO2 plane in a simple
environment without any vortex lattice and/or stripe order.Comment: 4 pages, 4 figures. To be published in Phys.Rev.Let
A New Iron Pnictide Oxide (Fe2As2)(Ca5(Mg,Ti)4Oy) and a New Phase in Fe-As-Ca-Mg-Ti-O system
A new layered iron arsenide oxide (Fe2As2)(Ca5(Mg,Ti)4Oy) and its structural
derivative were found in the Fe-As-Ca-Mg-Ti-O system. The crystal structure of
(Fe2As2)(Ca5(Mg,Ti)4Oy) is identical to that of (Fe2As2)(Ca5(Sc,Ti)4Oy), which
was reported in our previous study. The lattice constants of this compound are
a = 3.86(4) A and c = 41.05(2) A. In addition, another phase with a thicker
blocking layer was found. The structure of the compound and its derivative was
tentatively assigned through STEM observation as (Fe2As2)(Ca8(Mg,Ti)6Oy) with
sextuple perovskite-type sheets divided by a rock salt layer. The interlayer
Fe-Fe distance of this compound is ~30 A. The compound and its derivative
exhibited bulk superconductivity, as found from magnetization and resistivity
measurements.Comment: 9 pages, 7 figure
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