Magnetic measurements; Superconductors; Y-Ba-Cu-O; Ferromagnet; Bulk
Abstract :
[en] Bulk (RE)BCO materials can be used potentially as powerful permanent magnets. The magnetic flux distribution above a bulk HTS magnet, however, is strongly non-uniform (conic profile predicted by the Bean model) compared to the rather flat distribution above a ferromagnet. In the present work, we study how FeNi soft ferromagnetic alloys of different shapes can be combined with a bulk, large grain (RE)BCO superconductor (RE denotes a rare-earth element) to improve the distribution of trapped field at the surface or its average value through the volume of the sample. A FeNi ferromagnetic alloy was machined into pieces of various shapes (cylinders and rings) and attached to (i) the top surface of the bulk HTS cylinder to form bulk ferromagnet / superconductor (F/S) hybrids and (ii) to the top and bottom surfaces to form bulk F/S/F hybrids. The magnetic properties of each hybrid structure were measured under axial magnetic field at 77 K. Pick-up coils wound around the superconductor were used to measure the average magnetic induction inside the superconductor while the remnant induction distribution near the top and bottom surfaces was determined by miniature Hall probe mapping. The modifications of the hysteresis curves and flux distributions were analyzed by taking into account the ferromagnet intrinsic properties (intrinsic permeability, saturation) and geometrical properties (shape, size and volume). The results show that the effect of the ferromagnet increases with its volume. In presence of a ferromagnet, the superconductor hysteresis curve shows a combination of a diamagnetic and a ferromagnetic behaviour on which it is worth noting that (i) the bulk remnant magnetization increases and (ii) in the magnetic saturation regime of the ferromagnet, the magnetic effects of the superconductor and the ferromagnet are superimposed. The results also give evidence that flux lines curve through the ferromagnetic component, which produces a decrease of the self-demagnetizing field inside the superconductor.
Research Center/Unit :
SUPRATECS - Services Universitaires pour la Recherche et les Applications Technologiques de Matériaux Électro-Céramiques, Composites, Supraconducteurs - ULiège
Philippe, Matthieu ; Université de Liège - ULiège > Dép. d'électric., électron. et informat. (Inst.Montefiore) > Capteurs et systèmes de mesures électriques
Fagnard, Jean-François ; Université de Liège - ULiège > Dép. d'électric., électron. et informat. (Inst.Montefiore) > Capteurs et systèmes de mesures électriques
Wera, Laurent ; Université de Liège - ULiège > Dép. d'électric., électron. et informat. (Inst.Montefiore) > Capteurs et systèmes de mesures électriques
Dennis, Anthony; University of Cambridge > Engineering Department > Bulk Superconductivity Group
Shi, Yunhua; University of Cambridge > Engineering Department > Bulk Superconductivity Group
Cardwell, David A; University of Cambridge > Engineering Department > Bulk Superconductivity Group
Vanderheyden, Benoît ; Université de Liège - ULiège > Dép. d'électric., électron. et informat. (Inst.Montefiore) > Electronique et microsystèmes
Vanderbemden, Philippe ; Université de Liège - ULiège > Dép. d'électric., électron. et informat. (Inst.Montefiore) > Capteurs et systèmes de mesures électriques
Language :
English
Title :
Magnetic hysteresis cycle and remnant field distribution of bulk high temperature superconductor / ferromagnet hybrids
Publication date :
September 2013
Number of pages :
A0
Event name :
EUCAS 2013: European Conference on Applied Superconductivity
Event organizer :
ESAS
Event place :
Genova, Italy
Event date :
15 - 19 September 2013
Audience :
International
Funders :
F.R.S.-FNRS - Fonds de la Recherche Scientifique [BE] ULiège - Université de Liège [BE] FWB - Fédération Wallonie-Bruxelles [BE]