The ac linear (chi(0)) and nonlinear (chi(2)) susceptibilities of a fe
rromagnetic Ni have been studied near the Curie temperature, to clarif
y 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 cur
rents. From analysis of the frequency dependence of chi(0) and chi(2),
the method of eddy-current correction for chi(2) is found. Analysis o
f the critical behavior of chi(0) and chi(2) yields the critical expon
ents gamma = 1.333 +/- 0.008 and gamma(2) = 4.69 +/- 0.30.