X-ray magnetic-circular-dichroism spectra on the superparamagnetic transition-metal ion clusters Mn-12 and Fe-8 - art. no. 132413

X-ray magnetic-circular-dichroism (XMCD) spectra on the molecular superpara magnets [Mn12O12(CH3COO)(16)(H2O)(24)]. 2CH(3)COOH . 4H(2)O (in short Mn12) and [Fe8O2(OH)(12)(tacn)(6)]Br-2. 9H(2)O (in short Fe8) are presented. The XMCD measurements have been per-formed at the Mn-L-III,L-II edges in the M n-12 compound and at the Fe-L-III,L-II edges in the Fe8 compound. For Fe8 t he typical two-peak structure of Fe(III) compounds is found. For Mn12 and F e8, from the dichroic signals a very low or negligible [L-z] was obtained: to the best of our knowledge, this is the first direct experimental evidenc e of the quenching of the angular momentum by the crystal field in these sy stems. Quantitative analysis of the dichroic spectra for Fe8 yielded [L-z]/ [S-z] = 0.02(1).