Temperature dependent dielectric and magnetic properties of Gd and Ti co-doped BiFeO3 multiferroics

Abstract

Undoped BiFeO3, Gd doped Bi0.9Gd0.1FeO3, and Gd-Ti co-doped Bi0.9Gd0.1Fe1−xTixO3 (x = 0.10, 0.20) materials were synthesized to report their temperature dependent electric and magnetic properties. The structural analysis and phase identification of these multiferroic ceramics were performed using Rietveld refinement. The Rietveld analysis has confirmed the high phase purity of the 10% Gd-Ti co-doped Bi0.9Gd0.1Fe0.9Ti0.1O3 sample compared to that of other compositions under investigation. The major phase of this particular composition is of rhombohedral R3c type structure (wt% > 97%) with negligible amount of impurity phases. In terms of characterization, the magnetic properties of this co-doped ceramic system were addressed by applying substantially higher magnetic fields than that applied in previously reported investigations of this material system. Both the coercive fields and remanent magnetizations were higher for 10% Gd-Ti co-doped Bi0.9Gd0.1Fe0.9Ti0.1O3sample than those for other materials. The dependence of temperature on their magnetization behaviour have been investigated elaborately. Unexpectedly, the coercive fields of this multiferroic system increased with increasing temperature. The coercive fields and remanent magnetization were higher over a wide range of temperatures in 10% Gd-Ti co-doped Bi0.9Gd0.1Fe0.9Ti0.1O3 sample compared to those of other compositions. The magnetization versus applied magnetic field (M-H) hysteresis loops at different temperatures exhibited an asymmetric shift towards the magnetic field axes which indicated the presence of exchange bias effect in this material system. The hysteresis loops were also carried out at temperatures 150 K and 250 K by cooling down the sample from 300 K in various cooling magnetic fields. The exchange bias fields increased with cooling magnetic fields and decreased with temperature. The biasing fields were tunable by field cooling at temperatures up to 250 K. Additionally, the leakage current density has been measured to explore its effect on the ferroelectric properties of this multiferroic system. The outcome of this investigation suggested that the substitution of 10% Gd and Ti in place of Bi and Fe, respectively, in BiFeO3 significantly enhances its multiferroic properties. The improved properties of this specific composition was associated with homogeneous reduced grain size, significant suppression of impurity phases and reduction in leakage current density which was further asserted by polarization versus electric field (P-E) hysteresis loop measurements.