Fe3Ni-type chemical order in Fe65Ni35 films grown by evaporation: Implications regarding the Invar problem

Abstract

By use of Monte Carlo simulations of chemical ordering, magnetic ordering, and magnetovolume thermal effects and by reviewing the known effects of chemical order in the face-centered-cubic Fe-Ni alloy system, we show that the observations of Dumpich et al. [Phys. Rev. B 46, 9258 (1992)], who report unique Invar-composition ${\mathrm{Fe}}_{65}{\mathrm{Ni}}_{35}$ samples that exhibit Invar behavior despite being collinear ferromagnets with no deviation from the Slater-Pauling curve, are consistent with the effects of varying degrees of ${\mathrm{Fe}}_3\mathrm{Ni}$-type chemical order, which in turn are consistent with the sample preparation and treatment methods used. This allows us to make certain conclusive statements concerning models for Invar behavior and the nature of ${\mathrm{Fe}}_3\mathrm{Ni}.$