Evaluation of aging in electrodeposited permalloy memory wire

A method is described for evaluation of aging in electrodeposited Permalloy memory wire. The method is based on observation of electrical output degradation measured under conditions of nondestructive read-out (NDRO) following magnetic annealing treatment. The time required for a specified fractional decay of output is averaged for several wires and for both switching polarities. Data are presented showing that the time required for 25-percent output degradation t25obeys a temperature dependence indicative of a thermally activated process. The time constant and activation energy may be used to characterize the aging property for a particular condition of temperature and applied magnetic field. In well-stabilized wire the activation energy is about 1.7 eV, comparable to that observed in bulk diffusion processes. Auxiliary experiments showed that the typical mode of aging failure is insufficient write, which is accompanied by broadening of the switching threshold, and, more fundamentally, by a large increase in easy-axis dispersion.