Enhancement of ferromagnetic and dielectric properties in lanthanum doped BiFeO₃ by hydrothermal synthesis

Multiferroic Bi_1-xLa_xFeO₃ (x = 0.0, 0.1, 0.2, and 0.3) micro-particles were successfully synthesized by a hydrothermal technique. All the samples were phase pure crystallizing in a perovskite structure with a space group of R3c. XRD refinement revealed that the lattice parameters increased along with increase of La content, while the Fe-O octahedra became more distorted. It was found that the morphologies of as-obtained micron-sized particles turned from spheroidal to octahedral according to different doping levels. The dielectric constant of Bi_1-xLa_xFeO₃ sample increased after La doping, and reached the largest value for the sample of x = 0.2, both in low and high frequency range at room temperature. All the as-prepared samples exhibited magnetic moments starting above room temperature. It was found that the magnetic moment was significantly enhanced from 0.264 emu/g of BiFeO₃ to 0.658 emu/g of Bi_0.9La_0.1FeO₃ in a field of 3 T at 77 K. Both enhancements of ferromagnetic and dielectric properties possibly attribute to the changes of lattice parameters and Fe-O bond lengths caused by lanthanum substitution.