Enhanced Coupling Between Soft Ferromagnetism and Displacive Ferroelectricity in the Pb-Site Modified PbFe1/2Nb1/2O3

Abstract

Albeit having great potential toward unprecedented type of applications such as magnetoelectric (ME) sensors and memories, practically useful single-phase multiferroics that show large coupling between ferromagnetism and ferroelectricity at ambient temperatures are still lacking. Here, the discovery of a new type of perovskite ferroelectrics (Pb,M)(Fe_1/2Nb_1/2)O₃ (M = Fe, Co, Ni) is reported with a magnetically-active metal ion introduced into a cuboctahedrally-coordinated Pb position, which exhibits enhanced ME coupling owing to the development of simultaneous soft-ferromagnetism and lone-pair ferroelectricity persistent above room temperature. These Pb-site engineered (Pb,M)(Fe_1/2Nb_1/2)O₃ perovskites exhibit a ME coupling coefficient of ≈40–60 ps m⁻¹, a saturated electric polarization of 14–17 µC cm⁻² and a saturation magnetization of 0.15–0.3 µ_B f.u⁻¹. X-ray absorption spectroscopy combined with first-principles calculations demonstrates that the induced ferromagnetism originates from the ferromagnetic superexchange interaction coming from ≈90° bonding between the magnetic ions at the Pb site. The present discovery of the enhanced ME coupling in the Pb-site engineered perovskite ferroelectrics may provide unforeseen opportunities for applying conventional displacive ferroelectricity in the field of spintronics where ferromagnetism is essentially required.