Program Highlights

Magnetic Doping of Golden-Cage Clusters

X.C. Zeng, J. Bai
Nebraska MRSEC

L.M. Wang, L.S. Wang, W. Huang
Washington State University/PNNL

D. Schooss, M. Kappes
Karlsruhe, Germany

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 MAu₁₆^– 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 (5µ_B and 4µ_B), while Ni@Au₁₆^– has a lower spin (1µ_B), 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.

Fe, Co, and Ni atom in the gold-cage Au₁₆^–