Frequency Response of AC Susceptibility in Melt Textured YBCO Superconductors

Journal of Superconductivity 04/2005; 18(2):281-285. DOI: 10.1007/s10948-005-3382-7

ABSTRACT We have reviewed the scaling relations for frequency dependent AC susceptibility proposed by Lee. et al. and other contributions. Based on vortex glass analysis, we derived a scaling equation for the peak temperature of the imaginary part and ac magnetic field frequency f. The peak temperature Tp is found to obey: Tp = Cf1/(v(z–1))+Tg, where C is a constant, and Tg is the vortex glass temperature. The scaling relationship was applied to our melt textured YBCO superconductors, which was found in good agreement with the experimental data.

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    ABSTRACT: The real and imaginary parts of complex susceptibility values of bulk ceramic YBCO materials have been extracted at different frequencies and temperatures by measuring impedances using a single-coil swept-ac method. From these susceptibility components, the ac conductivity and its loss angle have been derived numerically. The dynamic and static critical exponents, z and ν obtained from the scaling of conductivity loss angle based on FFH’s vortex glass (VG) model were found to be in agreement with the values obtained by other workers, in different methods characterizing a continuous phase transition and revealing a stronger correlation in HTS materials. To verify their universality, it has been shown that the exponent values support the scaling features of ac-conductivity (or resistivity) very well and can scale susceptibility also at the proximity of critical temperature. It is highly expected that this simpler and straight forward method of extraction and evaluation of these critical exponents discussed here may be applicable to any other High Temperature Superconductors or other complex materials in bulk form.
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