Study of the spin dynamics in an iron cluster nanomagnet by means of Mossbauer spectroscopy

The spin dynamics of a cluster of four iron (III) ions characterized by a spin ground state of 5 and Ising anisotropy has been investigated by means of Mossbauer spectroscopy from 10 to 80 K. For T less than or equal to 35 K, spectra display a partially relaxed magnetic structure, while for higher temperatures, spectra are wholly relaxed. The trend of the probabilities of transition per unit time derived from the spectrum fittings is typical of an Orbach process or of a coupling with vibration modes in a narrow frequency range. According to an order-of-magnitude estimate, the relaxation mechanism should consist of modulations of the exchange interaction due to atom vibrations.