[seminar] Prof. dr. JOSIP HORVAT (IF, DANAS, 15 sati)

[IF Seminar]

Poštovani,

Podsjećamo Vas na današnji seminar na Institutu za fiziku
(15 sati u zgradi Mladen Paić), koji će održati Prof. dr. 
Josip Horvat sa Sveučilišta u Wollongong-u, Australia. 

Sažetak predavanja je u nastavku poruke.

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      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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Voditelji seminara IF-a (Ticijana Ban & Marko Kralj)