Multiferroic properties of Ba2+ and Gd3+ co-doped bismuth ferrite: magnetic, ferroelectric and impedance spectroscopic analysis

Enhanced magnetoelectric coupling is observed in bismuth ferrite samples, co-doped with non-magnetic Ba and magnetic Gd ions replacing Bi and Fe, respectively. Distortion in Fe-O octahedra has a significant effect on the magnetic properties of the samples. Ferromagnetic signature is found to increase significantly in the co-doped samples with respect to the only-Gd-doped sample both at 80 and 300 K. The co-doped samples show enhanced electric polarization as well as the highest resistivity at room temperature, which might be due to the reduction in the leakage current and oxygen vacancy in the compositions. An interesting correlation between the antiferromagnetic Neel temperature (T-N) of bismuth ferrite and the temperature-dependent dielectric constant is observed in all samples. Bi0.9Ba0.1Fe0.95Gd0.05O3 ceramic possesses maximum coupling between electric dipole and magnetic dipole with an estimated magnetodielectric effect MD ([epsilon(r)(H) - epsilon(r)(0)]/epsilon(r)(0)) similar to 380 at an applied field of 6 kOe. Impedance spectroscopy in the frequency range 40-10(7) Hz and temperature within 30-300 degrees C suggests that grain relaxation is dominant in the samples. Electrical parameters (such as capacitance and resistance) of the grains are determined using the real and imaginary parts of impedance (Z' and Z) and the electrical modulus (M' and M) plot. The results of electrical conductivity indicate a correlated barrier hopping conduction mechanism in the samples.