Magnetic moment and atomic volume in supersaturated Fe-Cu solid solutions: Ab initio calculations compared with experiments

The properties of nonequilibrium face-centered-cubic (fcc) and body-centered-cubic (bcc) Fe-Cu alloys were studied using the first-principles full-potential linearized augmented plane wave method within the generalized gradient approximation. The ab initio calculation results are compared quantitatively with the magnetic moment and atomic volume observed for mechanically alloyed Fe_xCu_100-x (x = 0 to 100) supersaturated bcc and fcc solid solutions. The calculations show that Cu alloying leads to a small enhancement of the magnetic moment of bcc Fe. The fcc Fe moment, on the other hand, experiences a more pronounced increase into a high-spin state upon alloying with Cu. It reaches approximately the same value as that in the bcc alloys for all Cu concentrations where fcc solutions are obtained in experiments, corroborating previous ab initio calculations using different methods. The magnetic moment increases are accompanied by an atomic volume expansion. Both the calculated moment and volume behavior are in good agreement with those measured for fcc and bcc Fe-Cu solutions. The magnetovolume expansion upon magnetic interaction between the alloyed Fe and Cu, rather than the positive heat of mixing, constitutes the primary reason for the atomic volume increase observed.