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We present calculations of the alternating current (ac) susceptibility in rectangular thin-film type-II superconductors, based on the critical-state model and on the minimization of magnetic energy. First, we simulate a homogeneous superconductor and give an analytical approximate expression for both real and imaginary parts of the ac susceptibility as a function of the amplitude of the ac applied field. Second, ac susceptibility is calculated in a superconductor composed by two parts connected by a region of lower critical-current density. We find two peaks can appear in the imaginary ac susceptibility although, because of the strong demagnetizing fields, these peaks overlap in some cases. Detailed explanations of the imaginary part of the ac susceptibility are given. [ABSTRACT FROM AUTHOR]

In order to better study the electromagnetic properties of superconducting films, the perpendicular critical-state ac susceptibility χ=χ′-jχ″ of a square superconducting film is numerically calculated using a magnetic energy minimization procedure as a function of the field amplitude Hm. The emphasis is put on the calculation accuracy of the low-Hm limit χ0 and the Hm at χ″=χm″. It is shown that after having accurate χ0, χ(Hm) of the square film can be accurately scaled from the analytical χ(Hm) of a thin disk. [ABSTRACT FROM AUTHOR]

Abstract: The perpendicular susceptibility of completely shielded elliptical and rectangular superconducting films with different aspect ratios has been calculated accurately. The obtained may be compared with the measured low-field limit of ac susceptibility to check the quality of superconducting films, and used as a scaling parameter to obtain field amplitude dependent complex critical-state ac susceptibility. [Copyright &y& Elsevier]

Abstract: The ac susceptibility of a type-II superconducting thin film divided into two halves by a narrow mid region with a smaller value of critical-current density is calculated by a model based on Bean’s critical-state model and energy minimization. Results are compared to measurements of ac susceptibility as a function of ac-field amplitude of artificial bicrystal-like films prepared by photolithography patterning a gridline of holes on epitaxial YBCO thin films. A qualitative agreement is found between calculated and experimental results. [Copyright &y& Elsevier]