Dielectric relaxation and magnetic behavior of bismuth-substituted yttrium iron garnet

Y3−xBixFe5O12 (x = 0–1.0) was prepared by solid state reaction. X-ray diffraction showed a gradual increase of lattice parameter with the Bi concentration, indicating that Bi had been incorporated into the lattice. Dielectric responses of the samples at room temperature increased initially at low Bi (x < 0.4) and then decreased rapidly at high Bi (x ≥ 0.6). Temperature dependence of dielectric constant showed a huge steplike increase at the temperatures between 20 and 200 °C, increasing with Bi. X-ray photoelectron spectroscopy revealed the presence of Fe2+ and Bi2+ in the samples, which might be responsible for the dielectric behaviors. An increase of coercivity and Curie temperature with Bi was observed. This was accompanied by a reduction of the saturation magnetization, whose variation with T follows a modified Bloch law.