Enhancement of Ferroelectricity and Magnetoelectric Effect of BiFeO 3 Thin Films on Membrane Structure
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0966-T03-13
Enhancement of Ferroelectricity and Magnetoelectric Effect of BiFeO3 Thin Films on Membrane Structure Seiji Nakashima, Kwi-Young Yun, Yoshitaka Nakamura, and Masanori Okuyama Division of Advanced Electronics and Optical Science, Department of Systems Innovation, Graduate school of Engineering Science, Osaka University, 1-3 Machikaneyama-cho, Toyonaka, 560-8531, Japan
ABSTRACT Multiferroic BiFeO3 thin films have been prepared on Pt/TiO2/SiO2/thick (200 µm) and membrane (15 µm) Si substrates by pulsed laser deposition (PLD) to confirm the influence of stress from substrate. The Si membrane was obtained by etching using reactive ion etching (RIE) until thickness is 15 µm. The X-ray diffraction peaks of BiFeO3 thin film on Pt/TiO2/SiO2/Si (15 µm) membrane substrate slightly shift to lower angles, compared to those on Pt/TiO2/SiO2/Si (200 µm) substrate. Ferroelectric hysteresis loops were also measured at 150 K before and after Si etching by RIE. The BiFeO3 thin film on the Pt/TiO2/SiO2/Si (15 µm) membrane structure shows remanent polarization (Pr) of 95 µC/cm2 for a maximum applied voltage of 18 V, which is larger than Pr = 71 µC/cm2 of BiFeO3 thin film on Pt/TiO2/SiO2/Si (200 µm) substrate at the same measurement conditions. Under magnetic field of 1.1 T, remanent polarization (Pr) of BiFeO3 thin film on Pt/TiO2/SiO2/Si (15 µm) membrane structure increased from 95 µC/cm2 to 101 µC/cm2 at 150 K. INTRODUCTION Recently, multiferroic materials such as YMnO3, BiFeO3 (BFO), BFO-BaTiO3 (solid solution) have much attracted considerable interest due to simultaneous existence of ferroelectricity, ferromagnetism (or antiferromagnetism) and ferroelastisity. Moreover, multiferroics showing interaction between dielectric and magnetic ordering are leading candidate for new types of devices using magnetoelectric effect. But it is necessary to obtain ferroelectric and ferromagnetic characteristics simultaneously and effective magneoelectric effect at room temperature (RT). Among many multifferoic materials, BFO is expected to show strong coupling of ferroelectric and antiferromagnetic ordering at RT because of its high Curie temperature (TC ~ 850 oC) and Neel temperature (TN ~ 370 oC) [1, 2]. Crystal structure of bulk BFO is rhombohedrally distorted perovskite belonging to space group of R3c with lattice parameter of a=0.562 nm and α = 59.35 o [3]. BFO single crystal is expected as a material showing large spontaneous polarization due to its largely distorted lattice at RT and ferroelectric instability of Bi3+ ion. However, it showed spontaneous polarization (Ps) only 3.5 µC/m2 and 6.1 µC/cm2 along [001] and [111] direction at 77K, respectively [4]. On the other hand, epitaxial BFO thin films grown on SrTiO3 single crystal show large polarization, which is larger than that of bulk BFO, and have monoclinic structure, which is different from bulk BFO case [5, 6]. It was also reported that polycrystalline BFO thin films on
Pt/TiO2/SiO2/Si deposited by chemical solution deposition (CSD) show large ferroelectric polarization
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