Room temperature multiferroicity in Aurivillius compounds Bi6Fe2−xNixTi3O18 (0≤x≤1)

We investigate the structural, magnetic, ferroelectric, and dielectric properties of Bi6Fe2−xNixTi3O18 (0≤x≤1). The coexistence of ferroelectricity and ferromagnetism were observed at room temperature for the Ni-doped samples. The ferromagnetism in Bi6Fe2−xNixTi3O18 can be understood in terms of spin canting of the antiferromagnetic coupling of the Fe-based and Ni-based sublattices via Dzyaloshinsky-Moriya interaction. Moreover, the substitution of Ni for Fe was effective for the enhancement of ferroelectric properties. The x=0.6 sample exhibits a maximum remnant polarization Pr of 37.8 μC/cm2 because of a lower leakage current. The rather large activation energy in the x=0 and 0.2 samples implies that the relaxation process may be not associated with the thermal motion of oxygen vacancies inside the bulk.