On the time dependence of the magnetic moment in high temperature superconductors

Investigation of the time dependence of the magnetic moment allows to get detailed informations about the pinning behaviour in high temperature superconductors (HTS). There are mainly two types of pinning barriers which both influence the time dependence in different way. First pinning centres in the bulk of the material, which act - despite of their special nature - in symmetrical way on flux entering or leaving the sample. This is in contrast to the action of surface barriers which have a strong asymmetrical influence. It is this different behaviour which allows to distinguish between both types of barriers and to investigate their properties separetely. This is shown for a HgBa2Ca2Cu3O8+x ceramics.