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.
