Anomalous Magnetic Hysteresis in the Microwave
Surface Resistance of MgB₂ Superconductor

A. Agliolo Gallitto, M. Bonura and M. Li Vigni

CNISM and Dipartimento di Scienze Fisiche ed Astronomiche,
Università di Palermo, Via Archirafi 36, I-90123 Palermo, Italy
E-mail: marco.bonura@fisica.unipa.it

Abstract - We report on field-induced variations of the microwave surface resistance in samples of MgB₂ produced by different methods. By sweeping the DC magnetic field up and down, we have detected magnetic hysteresis that can be ascribed to the different fluxon density at increasing and decreasing DC fields.in the critical state of the fluxon lattice. The hysteresis observed in the bulk samples has an unusual shape, which cannot be explained in the framework of the critical-state models.

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Received Novem,ber 26, 2007; accepted March 5, 2008.  Reference No. ST33; Category 2.
Paper accepted for Proceedings of EUCAS 2007; published in JPCS 98 (2008), paper # 012207