ISSN:
1089-7550
Quelle:
AIP Digital Archive
Thema:
Physik
Notizen:
A scheme is described for analytical calculation of critical-state magnetization M of superconductors in the geometry of long rectangular slabs and cylindrical specimens in a parallel magnetic field. The simplicity of the general scheme is demonstrated by deriving compact expressions for the ascending and descending field branches of M in the exponential model Jc=jc0 exp(−B/B0) and in the Kim, Hempstead, and Strnad model [Phys. Rev. 129, 528 (1963)], Jc=jc0/(1+B/B0). The analyses focus on the vertical width ΔM of large field magnetization hysteresis loops. While Bean's result [Phys. Rev. Lett. 8, 250 (1962)], Jc∝ΔM, today is used extensively to infer the critical current, it is well known that the method lacks consistency when a field dependence is seen in ΔM. For the two models it is shown explicitly that in the expansion of the functional relation ΔM(Jc), Bean's result corresponds to the lowest-order term. Also to the next order in the functional expansion we find a unifying form of expressing the model behaviors. This term contains the second derivative of J2c(B) with a prefactor that depends on the sample geometry. A model-independent proof for the two first terms in the expansion of ΔM(Jc) is also given, which allows the significance of size and shape, i.e., thickness and aspect ratio, to be discussed on a general basis. New methods to extract Jc from ΔM data, one of them without having to invoke specific critical-state models, are indicated. © 1995 American Institute of Physics.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1063/1.358576
