In this work, we studied the effect of heterovalent Ca, Sr, Pb, and Ba substitution on the crystal structure, dielectric, local ferroelectric, and magnetic properties of the BiFeO3 multiferroic perovskite. Ceramic solid solutions with the general formula Bi0.7A0.3FeO3 (A is a doping element) were prepared and characterized by x-ray diffraction, dielectric, piezoresponse force microscopy (PFM), and magnetic measurements. It is shown that the crystal structure of the compounds is described within the space group R3c, permitting the spontaneous polarization, whose existence was confirmed by the PFM data. Magnetic properties of the solid solutions are determined by the ionic radius of the substituting element. Experimental results suggest that the increase in the radius of the A-site ion leads to the effective suppression of the spiral spin structure of BiFeO3, resulting in the appearance of net magnetization.

Major-league magnetostriction: Magnetoelectric materials polarize in response to either electric or magnetic fields, making them attractive for data-storage applications. Long et al. discovered a ytterbium-based molecular magnetoelectric material with high magnetoelectric coupling (see the Perspective by Zhou and Han). An applied magnetic field strains the material, which changes its electrical properties. The required field is much lower than other magnetoelectric materials, and this work highlights the potential for using molecular materials in devices. Science , this issue p. 671 ; see also p. 627

Room-temperature crystal structure, local ferroelectric, and magnetic properties of the ${\text{Bi}}_{1-x}{\text{Gd}}_x{\text{FeO}}_3$ $\left(x=0.1,0.2,0.3\right)$ polycrystalline samples have been investigated by x-ray diffraction, piezoresponse force microscopy, and magnetometry techniques. Performed measurements have revealed a sequence of the composition-driven structural phase transitions $R3c\to Pn{2}_{1}a$ (occurs at $x\sim 0.1$ ) and $Pn{2}_{1}a\to Pnma$ (takes place within the concentrational range of $0.2<x<0.3$ ). The latter structural transformation is attributed to the substitution-induced suppression of the polar displacements. Gd substitution has been shown to effectively induce the appearance of the spontaneous magnetization, thus indicating a promising way for improving multiferroic properties of antiferromagnetic ${\text{BiFeO}}_3$ .

${\mathrm{Bi}}_{1-x}{A}_x\mathrm{Fe}{\mathrm{O}}_3$ ceramics $(A=\mathrm{Ca},\mathrm{Sr},\mathrm{Pb})$ were sintered by conventional mixed oxide route. The crystallographic structure of all samples is characterized by the rhombohedral symmetry (space group $R3c$ ). The existence of switchable ferroelectric polarization is verified by piezoresponse force microscopy that is proven to be a useful technique in semi-insulating ferroelectrics. Magnetic properties of Ca and Sr-doped ceramics are found to reproduce the antiferromagnetic behavior of undoped $\mathrm{Bi}\mathrm{Fe}{\mathrm{O}}_3$ without any enhancement of the magnetization. On the contrary, Pb-doped compound demonstrates appearance of a weak ferromagnetism. It is thus shown that Pb doping of $\mathrm{Bi}\mathrm{Fe}{\mathrm{O}}_3$ is a promising way for preparing multiferroic materials.