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Grain geometry effect on the magnetic properties of a granular iron-based superconductor LaFeAsO1-xFx (Articolo in rivista)

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Grain geometry effect on the magnetic properties of a granular iron-based superconductor LaFeAsO1-xFx (Articolo in rivista) (literal)

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Massimiliano Polichetti1, Danilo Zola1,3, Jian-Lin Luo2, Gen-Fu Chen2, Zheng Li2, Nan-Lin Wang2, Canio Noce1 and Sandro Pace1 (2012)
Grain geometry effect on the magnetic properties of a granular iron-based superconductor LaFeAsO1-xFx
in Superconductor science and technology (Print); IOP Publishing Ltd., Bristol BS1 6BE (Regno Unito)
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Massimiliano Polichetti1, Danilo Zola1,3, Jian-Lin Luo2, Gen-Fu Chen2, Zheng Li2, Nan-Lin Wang2, Canio Noce1 and Sandro Pace1 (literal)

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1 Dipartimento di Fisica 'E R Caianiello', Università di Salerno and CNR-SPIN, Unità di Salerno, via Ponte don Melillo, I-84084 Fisciano (SA), Italy 2 Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, People's Republic of China 3 Present address: ENEA-Agency New Technology, Energy & Sustainable Economy Development, Optical Coatings Group, Via Anguillarese 301, I-00123 Rome, Italy (literal)

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Grain geometry effect on the magnetic properties of a granular iron-based superconductor LaFeAsO1-xFx (literal)

Abstract

We have studied and compared the magnetic response of LaFeAsO0.92F0.08, in the form of granular bulk and powder, to the application of ac magnetic fields with different frequencies. The study of the third harmonics of the ac susceptibility has shown that the ac frequency plays an important role in the electromagnetic coupling of the grains in the granular sample. In particular, the characteristic harmonic response of the bulk sample at the highest frequency resembles the response of the unconnected grains of the powders, even at low frequencies. Moreover, the possibility of the occurrence of magnetic field focusing in the region between the grains, ascribed to both superconducting shielding and geometric effect of the grains, has been considered to explain the observed peak effect in the dc magnetization loops on the bulk sample. Although our investigation has be confined to the LaFeAsO0.92F0.08 granular, these results may be applied to any granular sample consisting of flat grains connected by weak links. Moreover, they also show that a peak effect in a granular superconductor can exist without necessarily invoke the existence of vortex dynamic processes (literal)
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