The microstructure and magnetic properties of PtMn-pinned top spin valves w
ere studied at various annealing temperatures. Magnetic properties were obs
erved to degrade with increasing temperature, with the exchange coupling H-
1 showing the fastest variation. The degradation did not appear to coincide
with structural changes or large-scale diffusion, It will be shown that th
e results are consistent with the grain boundary diffusion degradation mech
anism.