Multiple superhyperfine fields in a {DyFe2Dy} coordination cluster revealed using bulk susceptibility and 57Fe Mossbauer studies

A [(DyFe2Dy)-Dy-III(mu(3)-OH)(2)(pmide)(2)(p-Me-PhCO2)(6)] coordination cluster, where pmideH(2) = N-(2-pyridylmethyl)-iminodiethanol, has been synthesized and the magnetic properties studied. The dc magnetic measurements reveal dominant antiferromagnetic interactions between the metal centres. The ac measurements reveal zero-field quantum tunnelling of the magnetisation (QTM) which can be understood, but not adequately modelled, in terms of at least three relaxation processes when appropriate static (dc) fields are applied. To investigate this further, Fe-57 Mossbauer spectroscopy was used and well-resolved nuclear hyperfine structures could be observed, showing that on the Mossbauer time scale, without applied field or else with very small applied fields, the iron nuclei experience three or more superhyperfine fields arising from the slow magnetisation reversal of the strongly polarized fields of the Dy-III ions.