32 research outputs found
Enhancement of critical current density and vortex activation energy in proton-irradiated Co-doped BaFe2As2
The effect of proton irradiation in Ba(Fe0.93Co0.07)2As2 single crystals is
reported. We analyze temperature dependence of current density and normalized
flux relaxation rate in the framework of collective creep model. Glassy
exponent and barrier height for flux creep are directly determined by Maley's
method. Our model functions for barrier height and critical current density in
the absence of flux creep are explained by the superposition of \deltaTc- and
\deltal-pinning. We also approach true critical current density by means of
generalized inversion scheme, and the obtained result is in reasonable
agreement with our model function. Proton irradiation effect on temperature
dependence of current density and normalized relaxation rate can be summarized
as doubling of barrier height at the beginning of flux creep.Comment: 6 pages, 4 figures. To be published in Phys. Rev.
Magnetic-field periodic quantum Sondheimer oscillations in thin-film graphite
Materials with the mesoscopic scales have provided an excellent platform for
quantum-mechanical studies. Among them, the periodic oscillations of the
electrical resistivity against the direct and the inverse of the magnetic
fields, such as the Aharonov-Bohm effect and the Shubnikov-de Haas effect,
manifest the interference of the wavefunction relevant to the electron motion
perpendicular to the magnetic field. In contrast, the electron motion along the
magnetic field also leads to the magnetic-field periodicity, which is the
so-called Sondheimer effect. However, the Sondheimer effect has been understood
only in the framework of the semiclassical picture, and thereby its
interpretation at the quasiquantum limit was not clear. Here, we show that
thin-film graphite exhibits clear sinusoidal oscillations with a period of
about 1-3 T over a wide range of the magnetic fields (from around 10 T to 30
T), where conventional quantum oscillations are absent. In addition, the sample
with a designed step in the middle for eliminating the stacking disorder effect
verifies that the period of the oscillations is inversely proportional to the
thickness, which supports the emergence of the Sondheimer oscillations in the
quasiquantum limit. These findings suggest that the Sondheimer oscillations can
be reinterpreted as inter-Landau-level resonances even at the field range where
the semiclassical picture fails. Our results expand the quantum oscillation
family, and pave the way for the exploration of the out-of-plane wavefunction
motion.Comment: 17 pages, 5 figure
Magnetic relaxation and collective vortex creep in FeTeSe single crystal
We study the vortex dynamics in high-quality FeTeSe single
crystal by performing magnetization measurements of the screening current
density \emph{J} and flux creep rate \emph{S}. Temperature dependence of
\emph{S} shows a plateau in the intermediate temperature region with a high
creep rate 0.03, which is interpreted in the framework of the collective
creep theory. A crossover from elastic to plastic creep is observed. The glassy
exponent and barrier height for flux creep are directly determined by extended
Maley's method. \emph{J} with flux creep, obtained from magnetic hysteresis
loops, is successfully reproduced based on the collective creep analysis. We
also approach critical current density without flux creep by means of the
generalized inversion scheme, which proves that the \emph{l} and
\emph{T} pinning coexist in FeTeSe single crystal.Comment: 6 pages, 5 figure
Magnetic and transport properties of iron-platinum arsenide Ca10(Pt4-{\delta}As8)(Fe2-xPtxAs2)5 single crystal
We report superconducting properties of single crystalline
Ca10(Pt4-{\delta}As8)(Fe2-xPtxAs2)5 by X-ray diffraction, magnetization,
resistivity, and magneto-optical imaging measurements. The magnetization
measurements reveal fish-tail hysteresis loop and relatively high critical
current density Jc ~ 0.8\times105 A/cm2 at low temperatures. The exponential
temperature dependence of Jc, which arises from nonlinear effective flux-creep
activation energy, has been observed. Upper critical field determined by
resistive transition shows a relatively large anisotropy. The magneto-optical
images reveal homogenous current flow within the crystal.Comment: 6 pages, 6 figures, Accepted for publication in Phys. Rev.