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Published online by Cambridge University Press: 28 February 2011
We report a novel ac technique for characterizing the magnetic behavior of high-temperature superconductors. This technique is based on monitoring the spectrum of the magnetic response of these materials to small sinusoidal fields. A nonlinear magnetic behavior is indicated by the appearance of harmonic components in the spectrum. Measurements of these harmonics as a function of bias field, temperature and frequency provide valuable information about the processes of flux penetration, flux pinning and motion in these materials.