Stability, magnetic behavior, and chemical order of (Cox Fe1-x) N (N=5,13) nanoalloys

We report a systematic study of the stability, chemical order, and magnetic behavior of free-standing (Cox Fe1-x) N (N=5 and 13) nanoalloys as a function of the relative composition in the whole range. Calculations are performed within the ab initio density-functional theory (DFT) pseudopotential approximation as implemented in the SIESTA code. Within our DFT approach, the most stable five-atom Fe-Co nanoalloy is found at 40%25 of Co. A transition from icosahedral to biplanar hcp structure is obtained for N=13 as going from the Fe-rich phase to the Co-rich one, although the most stable composition corresponds to pure Co. High average magnetic moments per atom are obtained which decrease, in general, in 1 μB /N as increasing the Co concentration due to the substitution of Fe atoms by Co ones having one less d hole. Together with this decrease in the average magnetic moment, we find a slight enhancement of the local Co and Fe moments. Our results illustrate the rich structural and magnetic behavior of the Fe-Co alloys at the nanoscale and may be interesting for the design of magnetic grains which could be used in high-density storage devices. © 2009 The American Physical Society.

VIVO