  We study the magnetization and the spin dynamics of the Cr$_7$Ni ring-shaped
magnetic cluster. Measurements of the magnetization at high pulsed fields and
low temperature are compared to calculations and show that the spin Hamiltonian
approach provides a good description of Cr$_7$Ni magnetic molecule. In
addition, the phonon-induced relaxation dynamics of molecular observables has
been investigated. By assuming the spin-phonon coupling to take place through
the modulation of the local crystal fields, it is possible to evaluate the
decay of fluctuations of two generic molecular observables. The nuclear
spin-lattice relaxation rate $1/T_1$ directly probes such fluctuations, and
allows to determine the magnetoelastic coupling strength.
