1H-NMR studies on spin dynamics in molecular nanomagnet V15

1H-NMR study of a molecular magnet K6[V15As6O42(H2O)]8H2O (in short, V15) provides evidences for a gradual slowing of fluctuations of the V4+ spins with increasing magnetic field. The temperature and magnetic field dependence of 1/T1 is well explained by a model in terms of spin phonon interaction in the magnetic field region (H>2.7 T) where the ground state of the V15 cluster is S=32. On the other hand, the T1 data is not reproduced by the model in the low magnetic field region where the ground state is formed by two S=12 doubly degenerate states, suggesting importance of additional contribution to the spin dynamics of V4+ moments due to peculiarities of the S=12 triangle configuration in the V15 cluster.