  The disordered random-anisotropy magnetic nanoparticle systems with competing
dipolar interactions and ferromagnetic exchange couplings are investigated by
Monte Carlo simulations. Superspin glass (SSG) and superferromagnetic (SFM)
behaviors are found at low temperatures depending on the interactions. Based on
the mean field approximation, the Curie-Weiss temperature TCW = 0 is suggested
as the phase boundary between the SSG systems and the SFM systems, which is
convinced by the spontaneous magnetizations and relaxations. The magnetic phase
diagram is plotted.
