Phonon-induced relaxation in the Cr7 Ni magnetic molecule probed by NMR

We study the phonon-induced relaxation dynamics in the heterometallic Cr7 Ni ring. By assuming that spin-phonon coupling occurs through the modulation of local crystal fields, we investigate the decay of time correlations of molecular observables, such as fluctuations of the cluster magnetization. Single-crystal H1 nuclear magnetic resonance measurements have been performed for two orthogonal orientations of the applied magnetic field. The nuclear spin-lattice relaxation rate 1/ T1 probes fluctuations of specific molecular observables, thus allowing to determine the magnetoelastic coupling strength and to calculate the magnetization relaxation time as well as phonon-induced level lifetimes. The knowledge of these time scales is crucial to control the spin dynamics of the magnetic cluster in view of the potential technological applications. © 2010 The American Physical Society.