Using quantitative magneto-optical imaging to reveal why the ac susceptibility of superconducting films is history independent
Davi A. D. Chaves, J. C. Corsaletti Filho, E. A. Abbey, D. Bosworth, Z. H. Barber, M. G. Blamire, T. H. Johansen, A. V. Silhanek, W. A. Ortiz, M. Motta
DOI 10.1103/PhysRevB.109.104510 · Physical Review B
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Abstract
Measurements of the temperature-dependent ac magnetic susceptibility of superconducting films reveal reversible responses, i.e., irrespective of the magnetic and thermal history of the sample. This experimental fact is observed even in the presence of stochastic and certainly irreversible magnetic flux avalanches, which, in principle, should randomly affect the results. In this work, we explain such a paradoxical result by exploiting the spatial resolution of magneto-optical imaging. To achieve this, we successfully compare standard frequency-independent first-harmonic ac magnetic susceptibility results for a superconducting thin film with those obtained by ac-emulating magneto-optical imaging (acMOI). To demonstrate the possibilities of the acMOI technique, we further explore the experimental data. A quantitative analysis provides information regarding flux avalanches, reveals the presence of a vortex-antivortex annihilation zone in the region in which a smooth flux front interacts with preestablished avalanches, and demonstrates that the major impact on the flux distribution within the superconductor happens during the first ac cycle. Our results establish acMOI as a reliable approach for studying frequency-independent ac field effects in superconducting thin films while capturing local aspects of flux dynamics, otherwise inaccessible via global magnetometry techniques.
Source-reported materials — not catalogue approval
| Formula | Reported Tc (K) | Pressure (GPa) | Type |
|---|---|---|---|
| MoSi Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 7.3 | Pressure not reported | onset |
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