Proton NMR for Measuring Quantum Level Crossing in the Magnetic Molecular Ring Fe10

Abstract

The proton nuclear spin-lattice relaxation rate ${1/T}_{1}$ has been measured as a function of temperature and magnetic field (up to 15 T) in the molecular magnetic ring ${\mathrm{Fe}}_{10}({\mathrm{OCH}}_{3}{)}_{20}({\mathrm{O}}_{2}{\mathrm{CCH}}_{2}\mathrm{Cl}{)}_{10}$ (Fe10). Striking enhancement of ${1/T}_{1}$ is observed around magnetic field values corresponding to a crossing between the ground state and the excited states of the molecule. We propose that this is due to a cross-relaxation effect between the nuclear Zeeman reservoir and the reservoir of the Zeeman levels of the molecule. This effect provides a powerful tool to investigate quantum dynamical phenomena at level crossing.