Absolute spin magnetic moment of FeF2 from high energy photon diffraction

The magnetic spin structure factor of FeF2 has been directly determined fro m high energy magnetic x-ray diffraction at 115 keV photon energy. A pure s pin moment of mu = 401(5) mu (B) was observed, which agrees very well with the spin moment of the free Fe2+ ion and differs significantly from values of the total magnetic moment obtained by other methods. The magnetic phase transition of FeF2 has been carefully investigated and values for the criti cal exponent of the order parameter obtained by other techniques have been confirmed.