Critical phenomena are studied for the magnetic phase transition of a ferro
magnetic nanoparticle system with dipolar interactions and random anisotrop
y axes. The divergences of the nonlinear susceptibility and the longest rel
axation time are observed for a frozen magnetic fluid including uniform iro
n-nitride particles. These results indicate that the phase transition is si
milar to the spin glass transition. (C) 1999 Acta Metallurgica Inc.