Fast Field-Cycling NMR Study of Magnetomechanically Induced Relaxation Enhancement in Ferrogelatine

E. ANOARDO; F. BONETTO; D. PUSIOL

APPLIED MAGNETIC RESONANCE

Springer

Lugar: Berlin - Germany; Año: 2001 vol. 20 p. 563 - 578

0937-9347

We describe a field-cycling mgnetic resonance experiment aimed to study the nuclear spin-lattice realaxation in the simultaneous presence of an oscillating magnetic field and a magnetomechanically induced perturbation across the sample volume. The studied system is a gelatine doped with surfacted nanosize ferromegnetic particles. The spin system relaxes in coexistence with the magnetic interaction between the dopants and a weak external alternating magnetic field. Due to the interactions between the alternating field and the high magnetic moment of the dopants, a mechanical shaking of the particles becomes effective at low evolution fields. In this way, the particles act as local sonic sources, thus transmitting the vibrations to the gelic matrix where they are trapped. The impact produced on the molecular dynamics is observed through a magnetic resonence 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 piezoelectric transducer in direct contact with the sample.