Understanding local magnetic properties of dilute magnetic impurities in nonmagnetic hosts is of both fundamental and practical importance. Atomic metal clusters provide a unique medium for exploring local magnetism, as the cluster size, the number of valence electrons, and the local structures can be readily controlled and varied. In particular, a single magnetic atom trapped in a metallic cage (i.e., core/shell cluster) can be an ideal molecular model for dilute magnetic alloys. We have found the golden-cage Au16- cluster, which has a sufficiently large internal volume to encapsulate a foreign atom. We showed that the most stable structure of bimetallic MAu16- (M = Fe, Co, Ni) clusters is the core/shell M@Au16- structure, but with considerable distortions to the parent Au16- shell. Fe@Au16- and Co@Au16- are found to have similar structures with C2 symmetry, while a C1 structure is found for Au16Ni-. The 4s electrons are observed to transfer to the Au16 cage, whereas atomic-like magnetism due to the unpaired 3d electrons is retained for all the doped clusters. Fe@Au16- and Co@Au16- have high spins (5μB and 4μB), while Ni@Au16- has a lower spin (1μB), consistent with the stronger Ni-cage interactions [Phys. Rev. B 79, 033413 (2009)].
This research is supported by the National Science Foundation, Division of Materials Research, Materials Research Sciences and Engineering Program, Grant 0820521.
Co, and Ni atom in the gold-cage Au16-
