We calculate the magnetization relaxation in the short-time regime for
an ensemble of nanomagnets in the presence of a low frequency externa
l AC biasing field at temperatures lower than the magnetic anisotropy
energy of the individual nanomagnets. It is found that the relaxation
is strongly affected by AC fields with amplitude larger than that of t
he T-2 fluctuations in the nuclear field. This will allow experimental
probing of the nuclear spin relaxation mechanism.