Investigation of room temperature multiferroic properties in sol-gel derived gadolinium, cobalt doped BiFeO_3 nanoceramics

摘要

Detailed studies of structural, dielectric, magnetic, ferroelectric, and optical properties of a chemically sol-gel synthesized series of Bi_(1-x)Gd_xFe_(1-y)Co_yO_3 (x = 0, 0.1 and y= 0, 0.1) nanoceramics are presented. These nanoceramics attract attention as promising candidates for application as room temperature multiferroics in spintronics devices, exhibiting an optimistic set of properties. The average particle sizes of all the samples are calculated, and it was found to be ～45 nm from the Scanning Electron Microscopy image. The dielectric behavior of the prepared nanoceramics was investigated over a wide frequency (100 Hz-10~3 kHz) and a temperature (35-350°C) range. Interestingly, a low temperature dielectric anomaly is observed at around 170 °C for Bi_(0.9)Gd_(0.1)Fe_(0.9)Co_(0.1)O_3 due to the magnetoelectric coupling. A noticeably large value of dielectric constant (～990) and a low tan δ loss have also been observed for this nanoceramic at room temperature. The complex impedance spectroscopic analysis was also performed by plotting Nyquist plots, and the corresponding activation energies are evaluated from the Arrhenius fittings. Magnetization measurements of the samples reveal the presence of weak ferromagnetism due to surface spins as well as a noticeable improvement in the magnetic properties with Gd and Co doping. Ferroelectric properties have also been observed to be slightly improved because of doping, though it becomes somewhat lossy for Gd and Co doped samples. All the promising improved properties directly depend on the subsequent increase in the bandgap from 2.29 eV to 2.45 eV, with doping in the parent BiFeO_3 compound confirmed from UV-Vis spectroscopy.