Magnetic field distributions around superconducting strips on ferromagnetic substrates

Yasunori Mawatari

doi:10.1103/PhysRevB.77.104505

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Magnetic field distributions around superconducting strips on ferromagnetic substrates

Yasunori Mawatari

DOI 10.1103/PhysRevB.77.104505 · Physical Review B

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Abstract

The complex-field approach is developed to derive analytical expressions of the magnetic field distributions around superconducting strips on ferromagnetic substrates (SC/FM strips). We consider the ferromagnetic substrates as ideal soft magnets with an infinite magnetic permeability, neglecting the ferromagnetic hysteresis. On the basis of the critical state model for a superconducting strip, the ac susceptibility χ1′+iχ1″ of a SC/FM strip exposed to a perpendicular ac magnetic field is theoretically investigated, and the results are compared with those for superconducting strips on nonmagnetic substrates (SC/NM strips). The real part χ1′ for H0∕jcds→0 (where H0 is the amplitude of the ac magnetic field, jc is the critical current density, and ds is the thickness of the superconducting strip) of a SC/FM strip is 3∕4 of that of a SC/NM strip. The imaginary part χ1″ (or ac loss Q) for H0∕jcds<0.14 of a SC/FM strip is larger than that of a SC/NM strip, even when the ferromagnetic hysteresis is neglected, and this enhancement of χ1″ (or Q) is due to the edge effect of the ferromagnetic substrate.