Fast-field-cycling NMR study of magnetomechanically induced relaxation enhancement in ferrogelatine

We describe a field-cycling magnetic resonance experiment aimed to study th e nuclear spin-lattice relaxation in the simultaneous presence of an oscill ating magnetic field and a magnetomechanically induced perturbation across the sample volume. The studied system is a gelatine doped with surfacted na nosize ferromagnetic particles. The spin system relaxes in coexistence with the magnetic interaction between the dopants and a weak external alternati ng magnetic field. Due to the interaction between the alternating field and the high magnetic moment of the dopants, a mechanical shaking of the parti cles becomes effective at low evolution fields. In this way, the particles act as local sonic sources, thus transmitting the vibrations to the gelic m atrix where they are trapped. The impact produced on the molecular dynamics is observed through a magnetic resonance relaxation experiment. Saturation of the proton magnetization produced by the alternating magnetic field is also discussed. Results are compared with the direct effects produced by a pure sonic perturbation at the same frequency, introduced by coupling a pie zoelectric transducer in direct contact with the sample.