Superior hybrid improper ferroelectricity and enhanced ferromagnetism of Ca3(Ti1-xCox)2O7 ceramics through the superexchange interaction

Ca 3 (Ti 1- x Co x ) 2 O 7 ceramics were prepared by a tartaric acid sol-gel method and sintered in an oxygen atmosphere. The introduction of Co 2+ /Co 3+ as acceptor dopants leads to the formation of more oxygen vacancies and defect dipoles in Ca 3 (Ti 1- x Co x ) 2 O 7 ceramics. Oxygen vacancy and defect dipoles lead to the transition of dielectric , leakage, and ferroelectric behaviors of Ca 3 (Ti 1- x Co x ) 2 O 7 ceramics. The coexistence of hybrid improper ferroelectricity and ferromagnetism at room temperature in Ca 3 (Ti 1- x Co x ) 2 O 7 ceramics has been successfully realized through the superexchange interaction of Co–O–Co. Ca 3 (Ti 1- x Co x ) 2 O 7 ceramics exhibit superior ferroelectricity (the remnant polarization is 3.29 μC/cm 2 ) and enhanced ferromagnetism (the remnant magnetization reaches 6.4×10 −3 emu/g). This strategy based on the introduction of transition metal ions with unfilled 3d shells at B sites is an important approach to realize novel room-temperature single-phase multiferroic materials for Ca 3 Ti 2 O 7 -based materials.