Mn substitution-induced revival of the ferroelectric antiferromagnetic phase in [Bi.sub.1-x][Ca.sub.x]Fe[O.sub.3-x/2] multiferroics

Room-temperature X-ray diffraction, piezoresponse force microscopy, and SQUID magnetometry measurements of the [Bi.sub.0.9][Ca.sub.0.1][Fe.sub.1-y][Mn.sub.y][O.sub.3] (0 [less than or equal to] y ≤ 0.5) ferromanganites have been carried out to illustrate the effect of B-site substitution on the crystal structure and multiferroic properties of the Ca-doped compound representing an intermediate ferroelectric and weak ferromagnetic phase of the [Bi.sub.1-x][Ca.sub.x]Fe[O.sub.3-x/2] perovskites. The Mn doping has been shown to restore multiferroic behavior specific to pure BiFe[O.sub.3]. Indeed, the 0.1 ≤ y ≤ 0.4 samples have been found to possess a single-phase rhombohedral structure compatible with the ferroelectric polarization and antiferromagnetism. Further increase of the Mn concentration stabilizes an orthorhombic structure typical of the high-pressure antiferroelectric phase of the Bi[Fe.sub.1-y][Mn.sub.y][O.sub.3] perovskites. These results, particularly important from the viewpoint of understanding the origin of weak ferromagnetism in the [Bi.sub.1-x][Ca.sub.x]Fe[O.sub.3-x/2] system, are discussed using a model accounting for the doping-related defect formation.