A study of Fe–Mn (32&percent; and 34.65&percent;) and Fe3Pt Invar alloys during the transition from bulk to ultrafine (3–20 nm) particles is done at room temperature by combined x-ray diffraction and Mo¨ssbauer spectroscopy techniques. The particles obtained by evaporation of foil or filings of bulk material in an Ar atmosphere at pressures from 0.16 to 50 Torr were rapidly quenched during their production. Mo¨ssbauer measurements confirmed the availability of two spin states in both Fe–Mn and Fe3Pt fcc particles like it has been observed in previous studies of fine Fe and Fe–Ni (30&percent;–35&percent;) particles. Various heat treatments of the Fe3Pt foil with the initial bcc structure made it possible to obtain its fcc modification in either the entirely ordered or the entirely disordered state. It was shown that the disordered fcc structure in a bulk sample could exist in two spin states (ferromagnetic and paramagnetic) whereas the ordered structure was only in a ferromagnetic state. ©1997 American Institute of Physics.