Time domain studies of training effects in Co/Cu/FeNi/FeMn spin valves

Abstract

The recovery and the relaxation behaviors of the exchange bias (HE) in a Co/Cu/FeNi/FeMnspin valve has been studied via point contact technique with high field scan rates ranging from 1050 to 13500 Oe/s. The evolution of the exchange bias with the number of field cycles(n) shows a one over the square root of (n) dependence as against ln(n) in a previous study. A recovery of the exchange bias when the field cycling is stopped has been observed and the recovery ratio (R) is found to be a function of the logarithm of the recovery time (log(t)) in agreement with previous studies. The relaxation time of the exchange bias is estimated to be 6.62, 20.85, 43.10, 109.02, and 297.24 s for 13500, 5400, 2700, 1350, and 1050 Oe/s respectively. The one over the square root of (n) dependence of HE and the log (t) dependence of R have been discussed using thermal activation model.