Magnetic properties of Co and Co-Ag alloys in equilibrium/nonequilibrium structures studied byab initiocalculations

Ab initio calculations predict that the magnetic moments of the metastable fcc and bcc Co are 1.63 and 1.69μB, respectively, which are greater than the 1.57μB value of the equilibrium hcp Co. For the Co-Ag system, ab initio calculations reveal that the CoAg₃, Co₃Ag, and CoAg alloys are energetically favored to be in D0₁₉, D0₁₉, 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 1.76μB in D0₁₉ Co₃Ag and $B2$ CoAg alloys, respectively, while reduced to 1.43μB in the D0₁₉ CoAg₃ 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.