Magnetoresistance and interlayer diffusion in PtMn spin valves upon postdeposition annealing

We report annealing time effects on the microstructural evolution and resultant magneto-transport property changes in Ta/NiFe/CoFe/Cu/CoFe/PtMn/Ta spin valves comprising PtMn layer thicknesses ranging from 10 to 30 nm. Postdeposition annealing was performed at 270°C up to 35 h, The blocking temperatures of samples with 20 nm PtMn and 30 nm PtMn layers were found to be 350°C and 400°C, respectively. The magnetoresistance and interlayer coupling field changes became large as annealing time increased, in particular, for samples with relatively thicker PtMn layers. The main cause of microstructural changes and property degradation was due to interlayer diffusion of atomic constituents such as Mn, most likely through grain boundaries. Light B doping (1 at. %) in both free and pinned CoFe layers was proven effective in terms of blocking diffusion processes.