Phase transitions of iron-nitride magnetic fluids

Phase transitions of magnetic fluids in the zero field were studied from th e viewpoint of static susceptibility and typical relaxation time in order t o distinguish between the transitions and the blocking phenomena. We used i ron-nitride magnetic fluids containing nearly uniform particles so as to re move the effects of particle-size distribution. In the densest sample, we o bserved the growth of ferromagnetic fluctuations and, in the diluted sample s, a temperature-induced first-order phase transition.