Field-induced slow spin relaxation in monoclinic Nd$_{2}$Ti$_{2}$O$_{7}$ single crystals

We report the ac susceptibility measurement in the paramagnetic state of the monoclinic Nd$_{2}$Ti$_{2}$O$_{7}$ single crystals. An unexpected slow spin relaxation is observed in the presence of a nonzero magnetic field. Such behavior is absent in zero field. Distinct features of the relaxation, including the intrinsic frequency on the order of 1 Hz, the field-, temperature- and spin dilution dependence, and its evolution under positive and negative pressures, indicate that the relaxation is associated with an unusual cooperative behavior involving spin correlations.