Study on magnetic and electric properties on multiferroic $BiFeO_3$ thin films

Abstract

Multifunctional oxide materials such as $BiFeO_3$ (BFO), $HoMnO_3$, $YMnO_3$, etc, have been widely investigated in recent years, because they exhibit the coexistence of (anti-) ferromagnetic and (anti-) ferroelectric phases. Thus, they provide the characteristics to control the electric polarization by means of a magnetic field and the magnetization by an electric field, which are called magnetoelectric effect. These properties make them attractive candidates for novel device applications in the emerging field of spintronics. Among them, BFO is the only possible candidate material which can exhibit magnetoelectric effect at room temperature because of a high ferroelectric Curie temperature $(\It{T_C})$ of ~ 1100 K and an antiferromagnetic -$N\acut{e}el$ temperature $(\It{T_N})$ of ~ 640 K. Most high-quality epitaxial BFO films have been obtained by Pulsed Laser Deposition (PLD). Although PLD is one of the most effective methods for the deposition of such multicomponent oxide materials, it is still not an industrially viable method because of a difficulty in producing large area films. The on-axis sputtering technique which is the most efficient industrial process is employed to obtain high-quality epitaxial BFO films. To characterize the electric properties of the films, the conducting oxide $SrRuO_3$ (SRO) layer with a thickness of 100 nm was deposited on a $SrTiO_3$ (STO) substrate as a bottom electrode and Pt top-electrode was prepared using a shadow mask with a $200-\mum$ diameter. The (00l) peaks of BFO without any other peaks related to Bi oxides and Fe oxides were clearly observed in (001) BFO/SRO/STO films from X-ray diffraction (XRD) data. To investigate the epitaxial growth and the structure of the films, a XRD reciprocal space map (RSM) around the (112) diffraction spots was obtained. The RSM data revealed that the films were epitaxially grown on the STO substrate and have a fully strained tetragonal phase and a monoclinic phase with an angular di...