Magnetic and dielectric properties of Ca-substituted BiFeO₃ nanoferrites by the sol-gel method

A multiferroic material can simultaneously show two or more basic magnetic properties, including ferromagnetism, antiferromagnetism, and ferroelectricity. BiFeO₃ is a multiferroic material with a rhombohedral distorted perovskite structure. Doping can reduce the volatility of Bi and greatly improve the magnetoelectric properties of BiFeO₃.

To investigate the influence of the doping content we used the following analytical methods: X-ray powder diffraction (XRD), scanning electron microscopy (SEM), microwave network analysis (PNA-N5244A), and the Superconducting Quantum Interference Device (Quantum Design MPMS) test.

With the increase of Ca²⁺ concentration in the solution, the grain size of Bi_{1- x}Ca _xFeO₃ becomes smaller, showing the role of Ca²⁺ ions as the dopant for fine grains. The calcination temperatures are the major causes for the saturated magnetization. The residual magnetization ( M_r) and the coercive force ( H_c) decrease linearly with the increase of x value, and due to the effect of Ca²⁺ substitution at Bi³⁺ sites, which causes the valence change of Fe and/or the oxygen vacancies.

The XRD result indicates that the diffraction peak emerges with the increase of Ca²⁺ and the main diffraction peak achieves a high angle. The best calcining temperature is 600 °C, and the morphology is very dependent on the calcining temperature.