234 research outputs found
Surface superconducting states in a polycrystalline MgB sample
We report results of dc magnetic and ac linear low-frequency study of a
polycrystalline MgB sample. AC susceptibility measurements at low
frequencies, performed under dc fields parallel to the sample surface, provide
a clear evidence for surface superconducting states in MgB.Comment: 4 pages and 5 figure
The internal magnetic field in superconducting ferromagnets
We have measured the nonlinear response to the ac magnetic field in the
superconducting weak ferromagnet Ru-1222, at different regimes of sample
cooling which provides unambiguous evidence of the interplay of the domain
structure and the vorticity in the superconducting state. This is {\em direct}
proof of coexistence of ferromagnetic and superconductive order parameters in
high- ruthenocuprates.Comment: 9 pages, 6 figure
AC conductivity of a niobium thin film in a swept magnetic field
We report the results of the measurement the ac conductivity of a Nb
superconducting thin film in a swept dc magnetic field. In the mixed state the
swept dc field creates vortices at the film surface which pass through the film
and form the observed ac conductivity. Vortex rate generation does not depend
on the value of the dc field and there is a large plateau-like region of dc
magnetic fields where the dissipation is approximately constant. A proposed
phenomenological model describes quite well the main features of the ac
response in these fields including its dependency on the sweep rate, ac
amplitude, frequency, and value of the second and third harmonics.Comment: 7 pages and 10 figures; Journal of Physics: Condensed Matter, 201
The low-frequency response in the surface superconducting state of ZrB single crystal}
The large nonlinear response of a single crystal ZrB to an ac field
(frequency 40 - 2500 Hz) for has been observed. Direct
measurements of the ac wave form and the exact numerical solution of the
Ginzburg-Landau equations, as well as phenomenological relaxation equation,
permit the study of the surface superconducting states dynamics. It is shown,
that the low frequency response is defined by transitions between the
metastable superconducting states under the action of an ac field. The
relaxation rate which determines such transitions dynamics, is found.Comment: 7 pages, 11 figure
The electromagnetic response of a superconducting ferromagnets
The electromagnetic response of the superconducting ferromagnets RuSr₂Gd₁.₅Ce₀.₅Cu₂O₁₀ (Ru–1222
Gd) in an ac magnetic field of finite amplitude is investigated. Taking into account weak links between granules
and magnetization of the magnetic sublattice, it is shown that the response of a sample in a superconducting
state with the fundamental frequency and frequency of the 3rd harmonic can be described by the
nonlinear equation for the macroscopic field. Generation of the harmonic at temperatures above superconducting
transition corresponds to Rayleigh`s mechanism. Using various regimes of a sample cooling, the internal
magnetic field determined by the magnetic sublattice was measured. This is direct evidence of the coexistence
of ferromagnetic and superconductive order parameters in high-Tc ruthenocuprates
Nonlinear magnetic response in ruthenocuprates
We have performed an investigation of the nonlinear magnetic response in
ruthenocuprates. A negative, diverging-like peak at the main magnetic
transition T_N in RuSr2RECu2O8 (RE = Gd, Y) indicates a possible canted
antiferromagnetic order. Another well defined feature above T_N points to a
blocking of superparamagnetic particles through the T^(-3) dependence of the
third harmonic at higher temperatures. Below T_N a nondiverging peak appears,
which is strongly affected by the addition of 10% of Cu ions in the RuO2
planes. In RuSr2RE(2-x)Ce(x)Cu2O10 the main magnetic transition T_M is
accompanied by two characteristic temperatures in the third harmonic of the ac
susceptibility, in agreement with recent studies from uSR and Mossbauer
spectroscopy. We find that the spin-spin correlation temperature is the same in
both families of ruthenocuprates.Comment: accepted for publication in EPJ
Tunable coaxial cavity resonator for linear and nonlinear microwave characterization of superconducting wires
We discuss experimental results obtained using a tunable cylindrical coaxial
cavity constituted by an outer Cu cylinder and an inner Pb-BSCCO wire. We have
used this device for investigating the microwave response of the
superconducting wire, both in the linear and nonlinear regimes. In particular,
by tuning the different modes of the cavity to make them resonant at exactly
harmonic frequencies, we have detected the power emitted by the superconducting
inner wire at the second- and third-harmonic frequency of the driving field.
The results obtained in the nonlinear regime, whether for the microwave surface
impedance or the harmonic emission, are qualitatively accounted for considering
intergrain fluxon dynamics. The use of this kind of device can be of strong
interest to investigate and characterise wires of large dimensions to be used
for implementing superconducting-based microwave devices.Comment: 14 pages, 6 embedded figures, accepted for publication in Supercond.
Sci. Techno
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