Observation of the peak effect at high fields in single crystalline YBa2Cu4O8

The peak effect in the magnetic hysteresis of an untwinned YBa2Cu4O8 single crystal has been measured at temperatures down to 5 K, using a high sensitivity susceptometer in pulsed magnetic fields up to 50 T. The peak effect is due to an increase of the flux pinning as the magnetic field increases and results in a magnetisation hysteresis loop in the shape of a fishtail. The observed peak in the M(H) curve shows a clear temperature dependence in that the field Bmax at which the peak occurs increases with decreasing temperature. (orig.)