RELAXATION AND SCALING OF MAGNETIZATION AROUND THE FISHTAIL MINIMUM IN DYBA2CU3O7 SINGLE-CRYSTAL WITH COLUMNAR TRACKS

Conventional and dynamic relaxation processes and scaling properties o f the magnetic hysteresis loops (MHL) were studied on a Pb-ion irradia ted DyBa2Cu3O7-delta Single crystal by means of the torque magnetometr y. The columnar pinning structure produced by irradiation enhanced con siderably the induced critical current density and caused the high-fie ld part of the MHL to be field-independent up to B greater than or equ al to 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 relaxatio n rate and the MHL shape and point to quite different relaxation regim es-at high and low fields. Correspondingly, the scaling of the MHLs in both field ranges is different. This behaviour is modelled by two sep arable contributions to the MHL, one being active mainly at high field s and the other at low fields (central peak). Possible origins of thes e two contributions are discussed.