  We analyze the effects of the environment on the spin tunneling process of
paramagnetic and superparamagnetic particles and conclude that the non assisted
macroscopic tunneling rate is hardly affected in such case, but other more
effective (phonon mediated) processes change the magnetization state of the
particle. We conclude that for both, paramagnetic and superparamagnetic
particles, the decoherence time scale is extremely short (~ 10^(-8..-16)seg),
indicating thar coherent tunneling should be strongly suppressed in favor of
incoherent tunneling, i.e., the population of higher levels with subsequent
decay.
