Ferroelectric and Ferromagnetic Properties of BiFeO 3 Thin Films Deposited by Pulsed Laser Deposition

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C11.52.1

Ferroelectric and Ferromagnetic Properties of BiFeO3 Thin Films Deposited by Pulsed Laser Deposition Kwi-Young Yun1, Minoru Noda1, Masanori Okuyama1, Hiromasa Saeki2, and Hitoshi Tabata2 1 Division of Advanced Electronics and Optical Science, Department of Systems Innovation, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan 2 The Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka 567-0047, Japan

ABSTRACT BiFeO3 thin film has been prepared on Pt/TiO2/SiO2/Si substrate at a temperature as low as o

450 C by pulsed-laser deposition. The BiFeO3 thin film is perovskite single-phase, while any nonperovskite phase, such as orthorhombic Bi2Fe4O9, is not included. Dielectric constant of the film is 87, dielectric loss is 0.03, and leakage current density is low. The coexistence of ferroelectricity and ferromagnetism has been confirmed by means of the P-E and M-H hysteresis characteristics. The BiFeO3 thin film shows a well-saturated hysteresis loop with twice the remanent polarization 2Pr = 54 µC/cm2 and coercive field 2Ec = 100 kV/cm for a maximum applied electric field of 100 kV/cm, and also shows a saturated weak ferromagnetic hysteresis loop, as well as a small remanent magnetization with 2Mr = 0.6 emu/cm3 and 2Hc = 200 Oe for a maximum magnetic field of 10 kOe at room temperature.

INTRODUCTION In recent years, perovskite type oxide materials including ferromagnetic elements, such as BiFeO3, BiMnO3 and BaFeO3 etc., exhibit ferroelectric and ferromagnetic properties simultaneously, have attracted much attention, not only for possible application in practical electronic devices, but also from the view point of material science [1-4]. The coexistence of ferroelectric and ferromagnetic ordering makes it multiferroic materials. Especially, BiFeO3 (BFO) is reported to exhibit antiferromagnetic ordering with Néel temperature (TN ~310oC) and ferroelectric ordering with Curie temperature (TC ~850oC) [1,5]. A ferroelectric hysteresis loop of BFO single crystal with Pr of 3.5 µC/cm2 due to the electron polarization of Bi3+ has been confirmed at liquid nitrogen temperature [6]. In addition, BFO is known to have a G-type antiferromagnetic structure and weak ferromagnetic ordering [7,8]. However, one of the major problems of BFO thin films is low electrical resistivity and has

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affected the measurement of ferroelectric and/or ferromagnetic properties at room temperature (RT). The relatively high conductivity of BFO is attrituted to valence fluctuation of Fe ions (Fe3+ to Fe2+), creating oxygen vacancies for charge compensation. To overcome this obstacle, a recent study has been focused on solid solutions of BFO with other perovskite materials, such as BaTiO3 and PbTiO3 [9,10]. From our other observation, we have observed reduction of the current density in BFO thin films through controlled oxygen pressure, and the films show well-saturated ferroelectric hysteresis loop with twice the remanent polarization 2Pr = 71 µC/cm2 [11]. Recently, a fe

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