Flux Dynamics Effects in Superconducting Compacted Platinum Powders

Abstract

We have performed measurements of the complex magnetic ac susceptibility of superconducting compacted platinum powders at temperatures 0.1≲T≲10 mK with different ac excitation frequencies in the interval 5 Hz≲ω/2π≲10 kHz and with different excitation field amplitudes at 0.006≲bAC≲2 μT. The dependence of the ac susceptibility on the excitation field amplitude permits to determine the intergranular critical current density jc whereas the frequency dependence reflects the flux dynamics. By comparing the experimental results with theoretical predictions we identify flux flow, flux pinning and flux creep effects in the regimes of intra- and intergranular superconductivity. The possible impact of these effects on the superconducting parameters like jc of the samples is discussed.