Improved ferromagnetism and magnetodielectric properties of relaxor ferroelectric Ba4-xCaxNd2Fe1.5Co0.5Nb8O30 ceramics with tungsten bronze structure

Abstract The structural, magnetic, dielectric and magneto-dielectric properties of tungsten bronze Ba4-xCaxNd2Fe1.5Co0.5Nb8O30 (0 ≤ x ≤ 0.9) were investigated. All the samples can be indexed with the tetragonal structure and the space group of P4bm. The incorporation of Ca ions improves the structural distortion and promotes the grain’s growth. The magnetic curves at 300 K indicate the superposition of ferromagnetic (FM) and antiferomagnetic (AFM) state in all the samples, the observed FM phase can be attributed to the spin canting of AFM coupling of Fe- and Co-based sublattices. The Ca-doped samples exhibit an improved FM state due to large lattice distortion. The dielectric constant in anomaly region obeys well with Curie-Weiss law with γ = ∼1.6, implying that all the samples are relaxor ferroelectrics. The dielectric loss relaxations obey with Vogel-Fulcher relation and can be ascribed to the local polarization fluctuation induced by chemical heterogeneities. In addition, the relative change in magnetic field dependent dielectric constant follows with the change in the square of magnetization M2, suggesting that the observed magneto-dielectric is caused by the intrinsic magnetoelectric (ME) coupling effect. These results manifest that tungsten bronze compounds may be the potential candidates for the application in ME devices.