  Spinel Fe3O4 nanoparticles have been produced through ball milling in
methyl-alcohol (CH3OH), aiming to obtain samples with similar average particle
sizes <d> and different interparticle interactions. Three samples having
Fe3O4/CH3(OH) mass ratios R of 3 %, 10 % and 50 % wt. were milled for several
hours until particle size reached a steady value (<d> ~ 7-10 nm). A detailed
study of static and dynamic magnetic properties has been undertaken by
measuring magnetization, ac susceptibility and M\"ossbauer data. As expected
for small particles, the Verwey transition was not observed, but instead
superparamagnetic (SPM) behavior was found with transition to a blocked state
at TB ~ 10-20 K. Spin disorder of the resulting particles, independent of its
concentration, was inferred from the decrease of saturation magnetization MS at
low temperatures. For samples having 3% wt. of magnetic particles, dynamic ac
susceptibility measurements show a thermally activated Arrhenius dependence of
the blocking temperature with applied frequency. This behaviour is found to
change as interparticle interactions begin to rule the dynamics of the system,
yielding a spin-glass-like state at low temperatures for R = 50 wt.% sample.
