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 s pin ground state of 5 and Ising anisotropy has been investigated by means o f 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 t emperatures, spectra are wholly relaxed. The trend of the probabilities of transition per unit time derived from the spectrum fittings is typical of a n Orbach process or of a coupling with vibration modes in a narrow frequenc y range. According to an order-of-magnitude estimate, the relaxation mechan ism should consist of modulations of the exchange interaction due to atom v ibrations.