Modulated microwave absorption study of relaxation effects in Bi2Sr2CaCu2Oy

An induced minimum in the microwave absorption is reported in powdered and granular samples of Bi2Sr2CaCu2Oy using magnetically modulated microwave absorption. The minimum is observed at the cooling field when the sample is cooled through Tc to low temperatures and also appears when the sample is held for a time in a steady field. The time evolution of the intensity of the signal shows a ln(t) dependence over the temperature range 6-50 K. The origin of the induced absorption minimum is discussed and is attributed to intergranular flux creep relaxation.