A domain wall is created halfway the thickness of a permalloy film (dimensions ℓ × b × d = 120 × 30 mm² × 9 μ m) by passing a 16 A current in the direction of the width b through the film. The equilibrium position of this wall is varied by an in-plane magnetic field and determined from 3D polarisation analysis after transmitting a polarised neutron beam (λ = 0.2 nm) through the film (at 8^{{ring operator}} to the beam). Over a small field interval the net precession of the polarisation vector ranges from - π to + π with little depolarisation, implying that the domain wall moves from frac(1, 4) to frac(3, 4) of the thickness. If the wall approaches closer to either surface, the beam is fully depolarised. These observations apply also to AC fields up to 1 kHz. This suggests that the film can be used as wavelength adaptable flipper.