Study of the multicritical point in the vortex phase diagram (H||c) of a weakly pinned crystal of YBa₂Cu₃O_7-δ

Abstract

dc magnetization studies on a high quality YBa₂Cu₃O_7-δ crystal show that the flux-line lattice melting line extends beyond the notional "tricritical point" in the intermediate field region (~10 T), which broadly agrees with a recent theoretical proposal. The magnetization hysteresis data reveal the presence of both the peak effect (PE) and the fishtail effect in isothermal scans in the temperature interval 66-75 K. The broad anomaly in the magnetization hysteresis observed at lower temperatures (T<50 K), splits into two well separated peaks above 65 K. The upper peak closely resembles the classical PE phenomenon and the locus of the peak fields shows a turnaround behavior. On the other hand, the lower peak progressively moves to smaller fields as T T_c.