Effect of Gd substitution on the crystal structure and multiferroic properties of BiFeO₃

The crystal structure, magnetic and local ferroelectric properties of polycrystalline Bi_1-xGd_xFeO₃ (x = 0.1, 0.2, 0.3) samples were investigated at room temperature. Gadolinium substitution was found to induce a polar-to-polar R3c → Pn2₁a structural phase transition at x ≈ 0.1. Increasing the content of the substituting element suppressed the spontaneous polarization in Bi_1-xGd_xFeO₃, resulting in a ferroelectric-paraelectric Pn2₁a → Pnma phase transition at 0.2 < x < 0.3. The substitution caused the appearance of a weak ferromagnetic moment. The data presented are consistent with the hypothesis that the most effective way to induce spontaneous magnetization in antiferromagnetic BiFeO₃ seems to be related to A-site substitution by rare-earth ions with a large difference in ionic radius with respect to Bi³⁺. The effect of the magnetically active Gd³⁺ substitution on the low-temperature magnetic properties of Bi_1-xGd_xFeO₃ samples is also discussed.