The weak magnetism of bismuth ferrites Bi1−xDyxFeO3 with x=0.0 to 0.40 is studied via the electron spin resonance (ESR) of X-band (9.53 GHz) at various temperatures. The g-factor of pure BiFeO3 is 2.0, which originates from its cycloidal spin structure; while for the doped Bi1−xDyxFeO3 samples with x>0.10, ESR spectra reveal a second phase with a different g-factor around 1, which is attributed to the homogeneous magnetized phase of Bi1−xDyxFeO3. The temperature dependent ESR data further suggest a picture of the doping-induced transformation from cycloidal to canted antiferromagnetic state.

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Infrared and Raman-scattering spectroscopies were employed to explore the lattice and spin dynamics of Bi1–xDyxFeO3 nanoparticles. With increasing substitution of Bi by Dy in the range of 0.00 ≤ x ≤ 0.40, we observe (1) evidence for an increase of local lattice distortion of the FeO6 octahedra, and significant changes of phonon parameters in the x = 0.15 sample, corresponding to the structural transformation from rhombohedral to orthorhombic, (2) the chemically substituted enhanced dielectric constant of 43.4 in the x = 0.20 sample, (3) the development of two-magnon excitations in Dy substituted samples, which sensitively gauges the modification of magnetic structures from a cycloidal spin to a homogeneous magnetized state, and (4) Dy substitution disrupts the lattice-spin interactions at high temperatures. These findings extend our understanding of tailoring the structural and magnetic properties of chemically substituted multiferroic nanoparticles and advance the technologically important development of these materials.

Abstract:The lead-free multiferroic ceramic of (1-x)Ba 0.70 Sr 0.30 TiO 3 (BST) + xBiFeO 3 (BFO) was synthesized by a conventional solid-state reaction method. The dielectric, ferroelectric and magnetic properties was studied. The X-ray diffractomentry (XRD) revealed that the ceramic formed a single perovskite structure. The results suggested that the remanent magnetization (Mr) reached to maximum when the BFO content is up to 0.05. The powder of the samples Mr = 70 memu/g when x = 0.05. The change of the electrical resistance with magnetic field of the (1-x)Ba 0.70 Sr 0.30 TiO 3 + xBiFeO 3 samples reached 25.6% when x = 0.03. The relative dielectric constant was reduced under magnetic field compared with no magnetic field and the change is 13.1% as x = 0.01. It is indicated that the lead-free multiferroic ceramic of (1-x)Ba 0.70 Sr 0.30 TiO 3 + xBiFeO 3 exhibited both ferroelectric and magnetic at room temperature. The ferroelectric and magnetic properties are derived from the displacement of magnetic atom iron and the change of the atomic spin state.