Thickness dependence of exchange bias and structure in MnPt and MnNi spin valves

We describe x-ray diffraction and magnetic measurements of annealed MnPt and NiMn spin valves as a function of MnPt (NiMn) film thickness. Thin films (≲5–10 nm) are not chemically ordered and hence not antiferromagnetic, which explains the lack of exchange coupling in these films. With increasing thickness, the L10 chemical order develops (through coexistence between fcc and L10 phases) and there is a strong correlation between chemical order and exchange coupling. The lack of chemical order in the thin films is likely due to a lack of nucleation sites for the L10 phase.