Giant isotope effect in the incoherent tunneling specific heat of the molecular nanomagnet Fe8

Abstract

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 inelastic. 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.

Replaced with version accepted for publication in Physical Review Letters

References in corpus (3)

• Magnetic long-range order induced by quantum relaxation in single-molecule magnets
• Nuclear spin dynamics in the quantum regime of a single-molecule magnet
• Magnetization Process of Single Molecule Magnets at Low Temperatures

Cited by in corpus (8)

• Magnetothermal properties of molecule-based materials
• Tunable dipolar magnetism in high-spin molecular clusters
• Radiation- and Phonon-Bottleneck-Induced Tunneling in the Fe8 Single-Molecule Magnet
• Dynamics and thermalization of the nuclear spin bath in the single-molecule magnet Mn12-ac: test for the theory of spin tunneling
• Dynamics of molecular nanomagnets in time-dependent external magnetic fields: Beyond the Landau-Zener-Stückelberg model
• Extended Debye Model for Molecular Magnets
• Energy Level Lifetimes in the Single-Molecule Magnet Fe_8 : Experiments and Simulations
• Microscopic Theory for the Markovian Decay of Magnetization Fluctuations in Nanomagnets