QUANTUM TUNNELING OF THE MAGNETIZATION IN AN IRON CLUSTER NANOMAGNET

We have investigated the;magnetic relaxation of clusters of eight iron ions characterized by a spin ground state of ten- and an Ising anisot ropy. Below 400 mK the relaxation rate is temperature independent sugg esting that tunneling of the magnetic moment across its anisotropy ene rgy barrier occurs. Using the anisotropy constants derived from EPR da ta, we can calculate-both the-crossover: temperature T-c and the expec ted tunneling frequency 1/tau. The field dependence of the relaxation shows evidence of resonant tunneling.