Magnetization, Magnetoelectric Effect, and Structure Transition in $\hbox{BiFeO}_{3}$ and $(\hbox{Bi}_{0.95}\hbox{La}_{0.05})\hbox{FeO}_{3}$ Multiferroic Ceramics

Magnetization, grain size, x-ray diffraction, and dielectric permittivity of BiFeO
₃
(BFO) and 5 mol% lanthanum-substitution BFO [(Bi
_0.9
BLa
_0.05
)FeO
₃
] ceramics have been carried out as a function of sintering temperature (910-950°C) BFO ceramic exhibits an antiferromagnetic behavior, whose magnetization curve is linear with the field at room temperature. A weak ferromagnetic behavior occurs in (Bi
_0.9
BLa
_0.05
)FeO
₃
(BLFO) ceramics at room temperature, in which remanent magnetization increases from 0.008 to 0.14 as sintering temperature raises from 910 to 950°C. This phenomenon can be correlated with the growth of grain size of BLFO ceramics, which grows with increasing sintering temperature. The dielectric permittivities of BFO and BLFO are about 33 and 57 at room temperature, respectively. The dielectric losses (tan δ) of BFO and BLFO ceramics vary respectively in the ranges of ~0.2-0.4 and ~0.002-0.004 below 150°C, indicating that 5 mol% La-substitution can efficiently reduce electric conductivity. A frequency-dependent and broad dielectric maximum was observed in both BFO and BLFO ceramics upon heating. This dielectric response is likely triggered by the antiferromagnetic-paramagnetic transition near the Neel temperature.