High-Field ac Susceptometer Design for Measurements of Superconducting Single Crystals and Results
The use of ac induction techniques involving ac mutual inductance bridges and variances thereof have been discussed in detail in Section I of this volume. As has been emphasized in Section I and elsewhere1–3, a wealth of information can be obtained from measurements of the complex ac magnetic susceptibility, χac(H,T)=χ′(H,T)-iχ″(H,T) where H is the total magnetic field acting on the sample and T its temperature. Examples of the utility of these measurements involving topics of current and significant interest are: (a) the study of the “loss” peak as demonstrated by a peak in plots of χH″(T) VS. T and its relationship to the onset of magnetic irreversibility4,5 and (b) the dependence on the frequency of the ac measuring field of the normal to superconducting transition temperature, Tc, as manifested by the change in χH′(T). Studies of this frequency shift allows one to determine pinning energies involved in thermally activated flux motion occuring in single crystals and multigrained bulk samples1,6.
KeywordsTotal Magnetic Field Secondary Coil Primary Coil Flux Creep Magnetic Irreversibility4
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- 3.K.-H. Müller, M. Nikolo, N. Sawides, and R. Driver, “Ac Susceptibility of High-Temperature Ceramic Superconductors: Critical State and Creep at Grain Boundaries and in Grains,” Proceedings of the 3rd International Symposium on Superconductivity, Sendai, Japan, 6-9 November, 1990, Advances in Superconductivity III, Springer-Verlag, Tokyo 1991.Google Scholar
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