[en] We have prepared polycrystalline Co₂FeSi thin films on a number of seed layers to optimize their structural and magnetic properties. Using a Cr/Ag combined seed layer, films have been produced with extremely low interfacial roughness (<1 nm) and controllable coercivities in the range 12–27 Oe. Such a structure would be suitable for the free layer in a spintronic device. Using a NiCr seed layer and IrMn as an antiferromagnetic layer a small exchange bias of ∼30 Oe has been achieved. However the use of a 0.5 nm Mn layer at the IrMn/Co₂FeSi interface increases the exchange bias (H_ex) to 375 Oe after annealing. This structure would be suitable for the pinned layer in a spintronic device. (paper)