Microstructure, dielectric and magnetic properties of Bi1-xGdxMnO3 ceramics

Abstract

The nominal compositions of Bi1-xGdxMnO3 (x = 0.00-0.12) ceramics were synthesized by conventional solid state reaction technique and their morphological, dielectric and magnetic properties were investigated. The field emission scanning electron microscopy images and their respective histograms demonstrate that due to the substitution of Gd, the average grain size was reduced with a narrow size distribution. Particularly, for 12 % Gd substitution the average size was reduced up to around ~200 nm which is much smaller than that of undoped BiMnO3 ceramic. The substitution of Gd also generated significant amount of oxygen vacancies and the oxygen vacancies were gradually increased with Gd doping concentration. Compared to the undoped BiMnO3, the dielectric constant was stable in Gd doped BiMnO3 ceramics over a wide range of high frequencies (104 to 108 kHz) by suppressing the dispersion at low frequencies. The substitution of Gd in place of Bi also reduced the dielectric constant, particularly at low frequencies. The reduction of dielectric constant at low frequencies in Gd doped BiMnO3 ceramics may be associated with the large amount of oxygen vacancies which was generated upon the substitution of Gd. The magnetization versus magnetic field hysteresis loops were recorded using a Vibrating Sample Magnetometer (VSM) at room temperature. Due to the substitution of Gd, the magnetic parameters like remanent magnetization and coercive fields were enhanced nominally. The enhanced magnetic properties might be associated with the high magnetic moment of Gd3+ ion as well as the structural distortion in the perovskite with change in Mn–O–Mn bond angle. An asymmetric shift both in the field and magnetization axes of magnetization versus magnetic field curves was observed. This indicates the presence of exchange bias effect in these compounds notably at room temperature. Finally, the temperature dependent zero field cooled (ZFC) and field cooled (FC) magnetization curves demonstrate a ferromagnetic to paramagnetic transition around ~ 45 K in BiMnO3. Below this phase transition temperature, there was a splitting between ZFC and FC curves which indicates the presence of a spin glass like state in undoped BiMnO3. Due to the substitution of 4 % Gd in BiMnO3, the ferromagnetic to paramagnetic transition was remain unchanged, however, the ZFC and FC curves were coincided with each other.