Multiferroic Materials The Bifeo <sub> 3 </ Sub> Sol - Gel Preparation And Magnetic Studies

Multiferroics are materials possessing a spontaneous polarization, magnetization, and piezoelectricity that can be switched on by an applied electric field and magnetic field, respectively. These compounds present opportunities for potential applications in information storage, spintronics, and sensors. Of particular interest is BiFeO₃, which exhibits the coexistence of ferroelectric and antiferromagnetic orders up to quite high temperature. Recently, it has been reported that both epitaxial and polycrystalline BiFeO₃ thin films with reasonably high resistivity show large polarizations. For example, (001) oriented thin films BiFeO₃ display a polarization of 90 μC/cm², comparable to the very popular ferroelectric system, Pb(Zr_xTi_1-x)O₃ (PZT), which has been studied for decades for applications in memory, transducers, and micro-electro-mechanical system (MEMS). An aspect of concern with the PZT system is its relative toxicity accruing from lead. BiFeO₃ provides an alternative choice of a Pb-free ferro/piezoelectric material, which is environmentally preferable. There are intense researches on the enhancement of the ferroelectric property for BiFeO₃; however, the magnetization is still small for its applications in information storage, spintronics, and sensors. In the recent years, there has been revival interest in GdMnO₃ because of its potential in novel magnetoelectric and magnetocapacitive devices. The fabrication of one-dimensional nanostructures of BiFeO₃ and GdMnO₃ is of fundamental importance in investigating size correlation of the basic physical properties of this material, with implications for device applications.The main results and conclusions in the dissertation can be summarized as following:1. Detailed studies of magnetization of Bi_0.9-xGd_xLa_0.1FeO₃ (x = 0.3, 0.5, 0.6, and 0.7) are reported. An abnormal negative magnetization appears in the temperature-dependent magnetization curves and the temperature-dependent coercive field shows a maximum in the vicinity of the compensation temperature where the total magnetization is zero. These results suggest that in the ferrimagnetic-like system the Gd and Fe magnetic sublattices are coupled...