Substitution-induced structural, ferroelectric and magnetic phase transitions in BI_1-xGd_xFeO₃ multiferroics

Investigation of room-temperature crystal structure, magnetic and local ferroelectric properties of polycrystalline Bi_1-xGd_xFeO₃ (x= 0.1, 0.2, 0.3) samples has been carried out. Gadolinium substitution has been found to induce a polar- to- polar R3c→Pn2₁a structural phase transition at x~0.1. Increasing content of the substituting element has been shown to suppress 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 has been found to cause appearance of the weak ferromagnetic moment. The presented data are consistent with the hypothesis that the most effective way to induce the spontaneous magnetization in antiferromagnetic BiFeO₃ should be related to the A-site substitution with the ions having 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.