Dielectric and magnetic properties in Co- and Nb-substituted BiFeO3 ceramics

Co- and Nb-substituted BiFeO3 polycrystalline ceramics were synthesized by a solid-state reaction, and their dielectric and magnetic properties were investigated. Co substitution increased the electrical resistivity of BiFeO3 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 BiFeO3 were similar to 85 and similar to 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) BiFeO3 into ferromagnetic. The magnetoelectric coupling was estimated by determining the changes in the dielectric constant with an external magnetic field. (c) 2007 Elsevier Ltd. All rights reserved.