Magnetic properties of Co and Co-Ag alloys in equilibrium/nonequilibrium structures studied by<i>ab initio</i>calculations

Abstract

Ab initio calculations predict that the magnetic moments of the metastable fcc and bcc Co are 1.63 and $1.69{\ensuremath{\mu}}_{B},$ respectively, which are greater than the $1.57{\ensuremath{\mu}}_{B}$ value of the equilibrium hcp Co. For the Co-Ag system, ab initio calculations reveal that the ${\mathrm{CoAg}}_{3},$ ${\mathrm{Co}}_{3}\mathrm{Ag},$ and CoAg alloys are energetically favored to be in ${D0}_{19},$ ${D0}_{19},$ and $B2$ structures, respectively, and all prefer to be ferromagnetic rather than paramagnetic. Moreover, the magnetic moments of Co atom are enhanced to 1.62 and $1.76{\ensuremath{\mu}}_{B}$ in ${D0}_{19}$ ${\mathrm{Co}}_{3}\mathrm{Ag}$ and $B2$ CoAg alloys, respectively, while reduced to $1.43{\ensuremath{\mu}}_{B}$ in the ${D0}_{19}$ ${\mathrm{CoAg}}_{3}$ alloy. The results seem to suggest that an expansion of average atomic volume would enhance the magnetic moment of Co, which, however, would be reduced by nonmagnetic element alloying. Interestingly, the predictions agree reasonably well with those obtained from experimental as well as theoretical studies.