Exchange coupling in Fe50Mn50/Ni81Fe19 bilayer: Dependence on antiferromagnetic layer thickness

We have determined the dependence of exchange coupling on the antiferromagnetic layer thickness (tAF) in FeMn/NiFe bilayers, where the FeMn layer varies from 0.5 to 32 nm, and the NiFe is constant at 30 nm. For tAF>3 nm, the exchange field Hex varies as (1/tAF)0.3 at both 80 and 300 K, whereas the coercivity is insensitive to tAF. The value of Hex displays a simple angular dependence of cos θ.