Irreversible high-field behavior in Invar at low temperatures

Further experiments have confirmed that the thermal expansion coefficient α for 35% Ni Invar is independent of magnetic field at low temperatures, so that , where is the forced magnetostriction coefficient. This and other evidence of irreversibility is briefly reviewed and compared with other recent data on some Fe-Ni-Co alloys. The evidence points to a freezing-in of a state of strain corresponding to higher temperatures, with the mechanism on a scale small compared to that of the domain structure. This is important in allowing discrimination against models of Invar which cannot provide such a mechanism.