The 3rd Harmonic AC Susceptibilities in the Grain Model of High- T c Superconductors

AC susceptibility measurement has been widely used to investigate the magnetic properties of high-Tc superconductors which is composed of the grains and their interconnecting links. Transport critical current density is low because of a grain structure. The fundamental AC susceptibility of the superconductors with the grain structure has been successfully simulated using the critical state model by Irie and Yamafuji and gave separately the critical current densities in both intra- and inter- grains. The 3rd harmonic AC susceptibilities with a real part χ3’ and an imaginary part χ3” are numerically calculated in the grain model to get more clear insight of the grain-link structure. The double peaks and the multi-transitions also appear in the simulated curves. The simulated results are satisfactorily compared with the measured characteristics of Sm-123 superconductors to give pinning penetration fields Bpg and Bpℓ of the grain and the link. Combining with the crystallographic investigation, the critical current densities Jcg and Jcℓ in the grain and the link can be estimated.