Magnetic destabilization of Ni{sub 7}Al

Previously unknown cubic ordered Ni{sub 7}Al and Cu{sub 7}Pt compounds have recently been theoretically predicted to be stable phases in the Ni-Al and Cu-Pt systems. While Cu{sub 7}Pt was subsequently synthesized and identified, Ni{sub 7}Al remains experimentally unobserved. Using first-principles total energy calculations, we reinvestigate the stability of this Ni{sub 7}Al compound. We find the stability of this compound to be qualitatively effected by spin polarization, ignored in previous calculations. The effect of ferromagnetism is to stabilize the two-phase mixture of Ni+Ni{sub 3}Al relative to the Ni{sub 7}Al compound such that the latter is stable in nonmagnetic calculations, but unstable when spin polarization is taken into account. This reversal of relative stabilities of Ni{sub 7}Al and Ni+Ni{sub 3}Al with magnetism also has a dramatic effect on the calculated Ni{sub 3}Al/Ni interfacial energy {sigma} and spin-polarized calculations lead to a positive value of {sigma}, which is in qualitative agreement with values obtained from precipitation experiments. {copyright} {ital 1999} {ital The American Physical Society}