Linear magnetoelectrics refer to those compounds in which ferroelectric (FE) polarization can be generated by applying the magnetic field. This scenario opens an additional avenue toward high-temperature magnetoelectric (ME) coupling that is achievable in a large class of relatively weak frustrated magnetic systems such as honeycomb antiferromagnets. It is, thus, urgent to unveil the physics underlying the linear ME coupling in these linear ME materials. We grow the single crystals of Mn4Nb2O9, a linear ME candidate with high magnetic ordering temperature, and carry out a set of structural, magnetic, and ME characterizations. An antiferromagnetic ordering with [001]-oriented moments at the Neel point TN = 109 K is identified together with magnetic field driven large electric polarization emerging at TN, due to the strong exchange striction dependent mechanism. The measured ME coupling tensor α fits well the magnetic symmetry −3′m′, consistent with the linear ME scenario. Furthermore, remarkable responses of FE polarization and magnetization to the magnetic field and electric field, respectively, are demonstrated.

BiFeO3 has been receiving continuous attention for its excellent ferroelectric and multiferroic properties. Nevertheless, the piezoelectricity as a complementary property of ferroelectricity remains less addressed for BiFeO3 at least in a single phase form. In this work, we investigate the piezoelectric behaviors of bulk Bi1−xNdxFeO3 ceramics, given that the Nd-substitution may trigger structural phase transitions from the R3c phase to the Pna21 phase and eventually toward the non-polar Pnma phase. It is revealed that the piezoelectric coefficient d33 does increase with the increasing Nd content x inside the R3c phase region. However, no d33-enhancement across the R3c–Pna21 boundary region and the Pna21–Pnma boundary region is identified, suggesting no positive correlation between the piezoelectric coefficient and the possible morphotropic phase boundaries. The observed d33-enhancement inside the R3c phase region should be attributed to the remarkably reduced domain size and release of pinned domain wall motion by defects.