Short Time Quantum AC Response of a System of Nanomagnets

We calculate the magnetization relaxation in the short-time regime for an ensemble of nanornagnets in the presence of a low frequency external AC biasing field at temperatures lower than the magnetic anisotropy energy of the individual nanornagnets. It is found that the relaxation is strongly affected by AC fields with amplitude larger than that of the T2fluctuations in the nuclear field. This will allow experimental probing of the nuclear spin relaxation mechanism.