Kinetics of pinned layer and free layer relaxation upon hard axis anneal of NiMn spin valves

We discuss the results of a systematic study of the magnetic stability of both free and pinned layers in NiMn based spin valves upon hard axis anneals at temperatures ranging from 120/spl deg/C to 200/spl deg/C. For the free layer, the relaxation of the anisotropy follows a T In(t) dependence, where T is the anneal temperature and t is the anneal time. By contrast, the rotation of the pinned layer unidirectional anisotropy angle does not follow a simple logarithmic time dependence. A further difference lies in the relaxation rate, which in these particular spin valves is much more rapid for the free layer than the pinned layer. Significant training effects are observed when the sample is subjected to repeated major easy axis loops. In addition to the well known shrinkage of the pinned layer loop, we find that the training is associated with a net rotation of the unidirectional axis be as much as 10 degrees.