NONLINEAR SUSCEPTIBILITY OF NI NEAR THE CURIE-TEMPERATURE

The ac linear (chi(0)) and nonlinear (chi(2)) susceptibilities of a ferromagnetic Ni have been studied near the Curie temperature, to clarify the feature of the magnetic phase transition. The first observation for the critical behavior of chi(2) in a pure ferromagnetic system has been made at low frequency measurement. The observed chi(2) at higher frequencies is affected extremely by the contribution of the eddy currents. From analysis of the frequency dependence of chi(0) and chi(2), the method of eddy-current correction for chi(2) is found. Analysis of the critical behavior of chi(0) and chi(2) yields the critical exponents gamma = 1.333 +/- 0.008 and gamma(2) = 4.69 +/- 0.30.