Power-law resistivity, magnetic relaxation and ac susceptibility

摘要

The nonlinear diffusion of magnetic flux into a superconducting sample can be studied by measuring the relaxation of the magnetisation after application of a step field or by measuring the ac susceptibility, (chi)(sub 1) and its third harmonic, (chi)(sub 3), or preferably both methods covering different time scales. Each has been analysed recently for a field-cooled sample of a material whose creep activation energy depends logarithmically on current density, J corresponding to a power-law relation between electric field, E and J. Here, results are compared, using a universal scaling depth. Maximum (chi)(sub 1)(double prime) (vert bar)(chi)(sub 3)(vert bar) and values occur, and also the magnetisation has relaxed to half its initial value when the scaling depth is comparable to the sample half-thickness. (ERA citation 19:031708)