Magnetic phase diagram of interacting nanoparticle systems under the mean-field model.

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 T(CW) = 0 is suggested as the phase boundary between the SSG systems and the SFM systems, which is evidenced by the spontaneous magnetizations and relaxations. The magnetic phase diagram is plotted.