Magnetic relaxation in magnetic hysteresis measurements in unirradiated and neutron irradiated La1.86SrO.14CuO4 single crystals

Implications of flux creep and collective pinning are considered for magnetic hysteresis measurements. A nonlinear activation energy is used to represent the effects of collective behavior over a wide range of temperatures and magnetic fields. This is found in experiment in agreement with the self organized critical state model. The effects of thermally activated flux motion complicates the hysteretic response for typical experimental time scales. The authors illustrate this behavior for unirradiated and neutron irradiated single crystals of La1.86SrO.14CuO4. Constricted hysteresis loops are observed in which the size of the magnetic hysteresis is exponentially decreasing with increasing applied field as a result of the nonlinear pinning potential Ueff(J,H,T). This is shown to account for an experimentally observed exponential temperature and field dependence in magnetization current density resulting from relaxation during the course of measurement. Exponential field dependence can be explained without resorting to alternate forms of Jc(H) in critical state models