抄録
The thermal expansion coefficient α of Fe–Ni (fcc) alloys was measured in the range from 800°C to room temperature. Below the Curie temperature Tc, the α−T curve exhibits an anomaly corresponding to the spontaneous volume magnetostriction ωs. The ‘paramagnetic’ thermal expansion coefficient αp below Tc was determined by the extrapolation of the α−T curve above Tc and the value of ωs was estimated from the difference between αp and α below Tc. The relation between ωs and the change of Tc with pressure was discussed. The αp vs. composition curve at a fixed temperature shows a minimum around the invar alloys. This minimum corresponds to the anomaly in the elastic moduli vs. composition curves. It is thus pointed out that the lattice energy must be considered in addition to the magnetic energy in discussing the origin of the invar properties.
