Relevance of magnetic instabilities to the phase stabilities of Fe alloys

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Abstract
Fe and its alloys exhibit magnetic properties that range from simple ferromagnetic ordering in the bcc phase to moment-volume instabilities in the fcc phase. In the present study we give an account of the stabilities of the structural phases of Fe and its alloys and discuss how the stability of a particular phase is related to the magnetic properties. We discuss the pressure-temperature phase diagram of Fe and the differences between the Gibbs free energies of its various structural phases. We extend the discussion to fcc Fe alloys and present results on polarized paramagnetic neutron scattering experiments in Fe-rich Fe-Ni. In particular we show evidence for the presence of transitions from low-spin to high-spin state and the reversal of the sign of the energy difference between these states as the fcc phase gains stability. The latter effect becomes a crucial entity in determining the phase stability of Fe alloys.