Chemically induced ferromagnetic spin coupling: Electronic and geometric structures of chromium–oxide cluster anions, Cr2On− (n=1–3), studied by photoelectron spectroscopy

Abstract

Dichromium oxide cluster anions, Cr2On− (n=1–3), were found to possess highly spin-polarized electronic structures, which were revealed by the measurements of photoelectron spectra and the analyses by the density-functional calculations. Their spin magnetic moments were as large as 9, 9, and 7 μB for n=1, 2, and 3, respectively, due to a ferromagnetic coupling between local spins on the chromium atoms. The ferromagnetic spin couplings were caused predominantly by a superexchange-type Cr–Cr interaction through an oxygen atom at the bridge site, where a significant mixing of Cr 3d with O 2p orbitals stabilized the ferromagnetic states. The high-spin characters of Cr2On− are in striking contrast to that of a pure chromium dimer, which is known to exhibit an antiferromagnetic spin coupling due to the strong Cr–Cr covalent bond. The present ferromagnetic spin couplings should, therefore, be induced by oxidation. These findings support a concept that a chemical reaction controls magnetic properties of molecules and clusters.