LOW-TEMPERATURE QUANTUM RELAXATION IN A SYSTEM OF MAGNETIC NANOMOLECULES

We argue that to explain recent resonant tunneling experiments on crys tals of Mn-12 and Fe-8, particularly in the low-T limit, one must invo ke dynamic nuclear spin and dipolar interactions. The low-T, short-tim e relaxation will then have a root t/tau form, where tau depends on th e nuclear T-2, on the tunneling matrix element Delta(10) between the t wo lowest levels, and on the initial distribution N(xi) of internal fi elds in the sample, which depends strongly on sample shape. We also gi ve results for the long-time relaxation. [S0031-9007(98)06470-9].