Flux dynamics and irreversibility in yba₂cu₃0₇with y₂bacu0₅inclusions and in single crystal yba₂cu₃0₇

We have measured the ac magnetic permeability response function μ= μ' + іμ " in melt-processed melt grown YBa₂Cu₃0₇with Y₂BaCu0₅inclusions (MPMG) and in single crystal YBa₂Cu₃O₇(SC) in applied magnetic fields up to 8 Tesla oriented either parallel or perpendicular to the crystalline c-axis. The ac response of the two samples has been mapped out as a function of temperature, frequency, ac field amplitude, dc applied field, and field orientation. The peak in the lossy part of the susceptibility ft" is used to probe the flux dynamics in the vicinity of the irreversibility line. The data are interpreted by comparison with expectations for an anisotropic vortex glass-to-liquid transition. The inferred melting lines as well as the frequency dependence and non-linear response are in overall agreement with the expected behavior. In the range of available parameters and variables we find the system to be in the solid vortex phase for Hlc since there is a strong H_aсdependence and only a weak frequency dependence on the temperature position of the loss peak. For Hс, the situation is reversed, and the loss peak depends only weakly on H_асand strongly on the frequency.