Relevance of magnetic instabilities to the phase stabilities of Fe alloys

Fe and its alloys exhibit magnetic properties that range from simple ferrom agnetic ordering in the bce phase to moment-volume instabilities in the fee phase. In the present study we give an account of the stabilities of the s tructural phases of Fe and its alloys and discuss how the stability of a pa rticular phase is related to the magnetic properties. We discuss the pressu re-temperature phase diagram of Fe and the differences between the Gibbs fr ee energies of its various structural phases. We extend the discussion to f ee Fe alloys and present results on polarized paramagnetic neutron scatteri ng experiments in Fe-rich Fe-Ni. In particular we show evidence for the pre sence of transitions from low-spin to high-spin state and the reversal of t he sign of the energy difference between these states as the fee phase gain s stability. The latter effect becomes a crucial entity in determining the phase stability of Fe alloys.