  Magnetic relaxation in large spin molecular paramagnets is often found to
behave as the square root of time at short times t. This behaviour was
explained by Prokofiev & Stamp as arising from dipole interactions between
molecular spins. However, as observed by Miyashita & Saito, the same behaviour
can arise from a different mechanism which, in the present work, is related to
hyperfine interactions. The Miyashita-Saito scheme is found to be possible at
short times if the nuclear longitudinal spin relaxation is very slow. In the
case of moderately slow nuclear spin relaxation, the electronic magnetization
variation is initially proportional to t, then to the square root of t and
finally to decay exponentially. This behaviour may be mostly expected in dilute
systems.
