Giant Isotope Effect in the Incoherent Tunneling Specific Heat of the Molecular NanomagnetFe8

M. Evangelisti, F. Luis, F. L. Mettes, R. Sessoli, L. J. de Jongh
2005 Physical Review Letters  
Time-dependent specific heat experiments on the molecular nanomagnet Fe8 and the isotopic enriched analogue 57Fe8 are presented. The inclusion of the 57Fe nuclear spins leads to a huge enhancement of the specific heat below 1 K, ascribed to a strong increase in the spin-lattice relaxation rate Gamma arising from incoherent, nuclear-spin-mediated magnetic quantum tunneling in the ground-doublet. Since Gamma is found comparable to the expected tunneling rate, the latter process has to be
more » ... . A model for the coupling of the tunneling levels to the lattice is presented. Under transverse field, a crossover from nuclear-spin-mediated to phonon-induced tunneling is observed.
doi:10.1103/physrevlett.95.227206 pmid:16384263 fatcat:4cyphevojzfd5kk6kmxknjs4au