Dielectric and magnetic properties in Co- and Nb-substituted BiFeO_3 ceramics

摘要

Co- and Nb-substituted BiFeO_3 polycrystalline ceramics were synthesized by a solid-state reaction, and their dielectric and magnetic properties were investigated. Co substitution increased the electrical resistivity of BiFeO_3 by 2 orders of magnitude, while Co and Nb co-substitution raised the resistivity by 6 orders of magnitude, which allowed the dielectric constant and dielectric hysteresis to be determined at room temperature. The room temperature dielectric constant and loss tangent in co-substituted BiFeO_3 were ～85 and ～0.02, respectively. The electric hysteresis loop was obtained in the co-substituted specimen, but the loop was not really saturated. Magnetic hysteresis loops were observed in substituted specimens, and Co and/or Nb substitution transformed anti-ferromagnetic (weak ferromagnetic) BiFeO_3 into ferromagnetic. The magnetoelectric coupling was estimated by determining the changes in the dielectric constant with an external magnetic field.