The liquid ferromagnet Co80Pd20 and its critical exponent γ

Abstract By means of a new electromagnetic levitation apparatus the magnetization of solid cobalt, Co80Pd20 and liquid undercooled Co80Pd20 was measured in an external field of up to 60 mT close to the critical temperature. From this the ferromagnetic Curie temperature of the liquid phase TC(l)=1251 K could be determined. Following the extrapolation method of Arrott–Belov–Kouvel and using a modified Arrott plot the zero field susceptibility was computed yielding the effective exponent γ(T). Extrapolation of T→TC resulted in a critical exponent of γ=1.42±0.05 for the liquid ferromagnet in accordance with the Heisenberg model. While the temperature-dependent behavior at T>TC for crystalline cobalt results in a monotonic decrease to the molecular-field value 1, the chemically disordered alloy Co80Pd20 shows a distinct, sharp maximum in γ(T). In comparison, liquid Co80Pd20 has a broad maximum well above TC as already known for amorphous ferromagnets.