Chemically induced ferromagnetic spin coupling:Electronic and geometric structures of chromium-oxide cluster anions,Cr_2O_n~- (n=1-3),studied by photoelectron spectroscopy

摘要

Dichromium oxide cluster anions,Cr_2O_n~-(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 mu_B 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-CFr interaction through an oxygen atom at the the bridge site,where a significant mixing of Cr3d with O2_p orbitals stabilized the ferromagnetic states.The high-spin characters of Cr_2O_n~- 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.