Magnetostatic critical-point phenomena of Fe

The magnetostatic critical-point phenomena of a highly pure polycrystalline Fe sphere (99.999% pure) have been first investigated by a vibrating sample magnetometer for the applied field from 0 to 8 kOe. The kink point locus was observed for the whole critical region. The critical temperature, the spontaneous magnetization, and the zero-field susceptibility were determined without data extrapolations. The Curie temperature and the critical indices were obtained to be: Tc=1042.98±0.02 K, β=0.352±0.005 for ε=4×10−5–6×10−3, γ=1.269±0.005 for ε=2×10−4–2×10−2, and δ=4.20±0.05. γ neither agrees with the 3d Ising model nor with the 3d Heisenberg model, and β fits between the two models. These indices satisfy the Griffith’s inequality, γ′⩾β(δ−1). The critical equation of state was given by the same form as that for Ni.