[seminar] Prof. dr. JOSIP HORVAT (IF, 09.04, 15 sati)
IF Seminar
seminar at ifs.hr
Thu Apr 2 15:34:52 CEST 2009
Poštovani,
Obavještavamo Vas o održavanju seminara na Institutu za fiziku
u četvrtak 9. travnja u 15 sati (u zgradi Mladen Paić), koji
će održati Prof. dr. Josip Horvat sa Sveučilišta u Wollongong-u,
Australia. Prof. Horvat je trenutno u posjeti prof. Babiću s
PMF-a s kojim ima zajednički UKF cooperability projekt:
<http://www.ukf.hr/default.aspx?id=18&projectid=63&prikaz=1>
Sažetak predavanja nalazi se u nastavku poruke.
Peak effect in MgB2/Fe superconducting wires:
interaction between superconductor and ferromagnet
Josip Horvat
School of Physics and Institute for Superconducting and Electronic
Materials, University of Wollongong, Australia
E-mail: jhorvat at uow.edu.au
Transport critical currents (Ic) in MgB2/Fe superconducting wires increase
with field in a well-defined field interval, followed by a decrease of Ic,
if the critical currents of these wires are beyond a threshold value. This
is referred to as the "peak effect". Similar effect has also been reported
for Bi2223/Ag tapes clad with iron sheath. This effect cannot be explained
by a mere magnetic shielding by iron sheath, because the peak effect occurs
at high fields where magnetic shielding is not effective any more.
Measurements of V-I characteristics imply that the re-magnetization of the
iron sheath by the transport current is an essential pre-requisite for the
peak effect. As a consequence of this re-magnetization, the magnetic domains
of the iron sheath do not seem to have a magnetization component perpendicular
to the superconductor/ferromagnet interface. However the resulting domain
walls do and they interact with magnetic vortices pinning them down. This
increased pinning is responsible for the increase of the Ic. Subsequent
decrease of Ic occurs as the density of domain walls decreases when the iron
approaches magnetic saturation, giving the observed peak effect. This scenario
is supported by magneto-optical imaging experiments reported recently, which
clearly show the interaction between the magnetic domain walls of a ferromagnet
and magnetic vortices of a superconductor.
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