Effects of trivalent gadolinium and cobalt co-substitution on the crystal structure, electronic transport, and ferromagnetic properties of bismuth ferrite

Abstract

Multiferroic trivalent gadolinium and cobalt co-substituted bismuth ferrite Bi0.95Gd0.05Fe1−xCoxO3(x=0, 0.05, 0.1, 0.15, 0.2) ceramics were prepared by rapid liquid phase sintering method. The results showed that all the peaks of X-ray Diffraction (XRD) for Bi0.95Gd0.05Fe1−xCoxO3 samples can be indexed according to the crystal structure of pure BiFeO3. XRD analysis revealed a phase transition in Gd3+ and Co3+ co-doped BiFeO3 when x was larger than 0.1. The Scan Electron Microscope (SEM) images indicated that Gd3+ and Co3+ doping significantly decreased the grain sizes of BiFeO3 ceramic. Gd3+ and Co3+ co-doping BiFeO3 enhanced the electrical properties with lower leakage current. The magnetic hysteresis loops and the magnetization were greatly improved in co-substituted specimens at room temperature. The Mr of Bi0.95Gd0.05Fe1−xCoxO3 (x=0, 0.05, 0.1, 0.15, 0.2) was 34, 60, 105, 103 and 180 times of that of BiFeO3 at 30kOe, respectively. All the samples exhibited ferromagnetic behavior at 750K and paramagnetic behavior at 900K, indicating a high temperature magnetic phase transition of BiFeO3 at 870K, which shifted to 780K by Gd3+ and Co3+ doping. This can be attributed to the Fe3+–O2−–Fe3+ super-exchange strength and the relative stability of the magnetic structure.