Czechoslovak Journal of Physics 46, 1615 (1996)

K. Rogacki, X. Zeng, P. Esquinazi, and B. Dabrowski

Abstract

We have measured the magnetic properties of YBa₂Cu₄O₈ crvstals in magnetic fields parallel and perpendicular to the CuO₂ planes with the vibrating reed, ac susceptibility and dc magnetization techniques. As a function of temperature we have observed a large enhancement of the pinning force at T_m that is approximated by a line B_m oc -1.2T [T/K] for fields parallel to the CuO₂ planes. This enhancement is accompanied by a minimum in the flux line lattice dissipation and is also observed in the ac susceptibility as an increase in the shielding capability. The peak effect is dependent on the magnetic history.