Relaxation and scaling of magnetization around the fishtail minimum in DyBa₂Cu₃O₇ single crystal with columnar tracks

Conventional and dynamic relaxation processes and scaling properties of the magnetic hysteresis loops (MHL) were studied on a Pb-ion irradiated DyBa₂Cu₃O_7-δ single crystal by means of the torque magnetometry. The columnar pinning structure produced by irradiation enhanced considerably the induced critical current density and caused the high-field part of the MHL to be field-independent up to B ≥ 7 T. The substantial change of the pinning structure shifted the appearance of the fishtail effect to higher temperatures and fields. The relaxation experiments confirm a correlation between the relaxation rate and the MHL shape and point to quite different relaxation regimes at high and low fields. Correspondingly, the scaling of the MHLs in both field ranges is different. This behaviour is modelled by two separable contributions to the MHL, one being active mainly at high fields and the other at low fields (central peak). Possible origins of these two contributions are discussed.