Analytical investigation of magnetic field distributions around superconducting strips on ferromagnetic substrates

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 ${\chi }_1^{\prime }+i{\chi }_1^{\prime \prime }$ 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 ${\chi }_1^{\prime }$ for $H_0/j_c{d}_s\to 0$ (where $H_0$ is the amplitude of the ac magnetic field, $j_c$ is the critical current density, and $d_s$ 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 ${\chi }_1^{\prime \prime }$ (or ac loss $Q$) for $H_0/j_c{d}_s<0.14$ 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 ${\chi }_1^{\prime \prime }$ (or $Q$) is due to the edge effect of the ferromagnetic substrate.

8 pages, 6 figures, submitted to Phys. Rev. B

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