SUPPRESSION OF MAGNETIZATION BY A SMALL TRANSVERSE AC MAGNETIC FIELD

One efficient method to investigate the vortex matter in the high-temperature superconductors is to measure the magnetization while shaking vortices by applying a transverse ac magnetic field, H_ac. When a small transverse H_ac is superposed with the dc magnetic field, the vortices will experience time-varying torque by ac field. This vortex shaking gives rise to effective reduction of pinning energy, which in turn gives rise to a rapid relaxation of the irreversible magnetization. This experimental approach has been used to study the nature of the anomalous magnetization peak in a N₂-annealed Tl₂Ba₂CuO single crystal. Shaking vortex unveiled the otherwise unobserved anomalous magnetization peak; when H_ac=0, no noticeable structure in the magnetization loop was observed, but with vortex shaking by H_ac, the magnetization loop deformed to exhibit the anomalous magnetization peak. The evolution of the anomalous peak with H_ac can provide a clue to the understanding of the underlying mechanism for the occurrence of the peak.