Structure and chemical order in Co–Rh nanoparticles

The 300 K structure of soft chemistry synthesized CoxRh1 - x (x = 0.2,0.5,0.75) particles, 1.7 to 2.5 nm large, has been determined by atomic-scale simulations using an interaction model fitted on both ab initio and experimental results. All the measured structural features, strongly different from the ones in the corresponding bulk alloys, have been consistently reproduced. Two major effects, i.e. a strong Co surface segregation and an expansion of the mean bond length, are demonstrated and both are consistent with the drastic enhancement of the magnetization observed in these clusters. Interestingly, the method also provides new insights into interpretation of the experimental results.