Relaxation time of the nanomagnetFe4

Abstract

The magnetic behavior of the molecular nanomagnet ${\text{Fe}}_{4}$ is very well simulated by a single-spin model Hamiltonian in a crystal field with $S=5$. The crystal-field parameters were determined from the inelastic neutron scattering spectra. Here we show that the quantum effects are crucial to understand the saturation of the relaxation time observed at very low temperature at variance with the standard master equation result that leads to an Arrhenius law at any temperature. Very deep downward spikes in correspondence to the anticrossing fields are found in the relaxation time vs field at low temperature. We compare our results with those obtained by previous approaches worked out to fit experimental data on ${\text{Mn}}_{12}$.