NEUTRON SPECTROSCOPY FOR THE MAGNETIC-ANISOTROPY OF MOLECULAR CLUSTERS

Neutron spectroscopy has been used to observe transitions between the energy levels for the 21 different orientations of the S = 10 spin gro und state of an octanuclear iron molecular cluster (Fe-8) exhibiting q uantum tunneling of the magnetization. The results obtained on nondeut erated samples provide the first direct measurement of the zero-field splitting in a large cluster nanomagnet. A reliable and accurate deter mination of the composition of the cluster's spin wave functions and t he spin-Hamiltonian parameters are deduced from the experimental obser vations, giving crucial information for the study of the macroscopic q uantum tunneling process. [S0031 -9007(98)07673-X].