Magnetic and electronic properties of hexairon(III) nanocluster with cyclic structure: a Moessbauer study

A molecular cluster containing a coplanar ring of iron(III) ions with spin 5/2 was investigated by Moessbauer spectroscopy. The iron spins are antiferromagnetically coupled so that the ground state has total spin S=0. Spectra in the absence of an applied magnetic field consisted of a quadrupolar doublet, the linewidth of which monotonically increased with the temperature. A quadrupolar splitting of about 0.35 mm/s was found. Calculations of the iron-orbital electronic populations were carried out and the quadrupolar splitting was estimated. Its value was in agreement with the experimental one. In addition, the trend of the linewidth was explained in terms of isotropic spin fluctuations. Spectra in the presence of a 4.5 T longitudinal magnetic field were also collected. The hyperfine field was obtained from their fitting. Differences with respect to the hyperfine field obtained from susceptibility data were also interpreted in terms of spin fluctuations