  The ZFC and FC magnetization dependence on temperature was measured for
BiFeO3 ceramics at the applied magnetic field up to H=10T in 2K-1000K range.
The antiferromagnetic order was detected from the hysteresis loops below the
Neel temperature TN=646K. In the low magnetic field range there is an anomaly
in M(H), probably due to the field-induced transition from circular cycloid to
the anharmonic cycloid. At high field limit we observe the field-induced
transition to the homogeneous spin order. From the M(H) dependence we deduce
that above the field Ha the spin cycloid becomes anharmonic which causes
nonlinear magnetization, and above the field Hc the cycloid vanishes and the
system again exhibits linear magnetization M(H). The anomalies in the electric
properties, which are manifested within the 640K-680K range, coincide to the
anomaly in the magnetization M(T) dependence, which occurs in the vicinity of
TN. We propose to ascribe this coincidence to the critical behaviour of the
chemical potential, related to the magnetic phase transition.
