Multiferroic and photovoltaic current properties of tetragonally strained BiFeO 3 thin films
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Multiferroic and photovoltaic current properties of tetragonally strained BiFeO3 thin films Hyun Wook Shin 1
&
Jong Yeog Son 1
Received: 24 November 2019 / Accepted: 10 July 2020 # Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Mn (5%) doped BiFeO3 (MBFO) thin films were epitaxially grown on La2/3Sr1/3MnO3/LaAlO3 substrates via pulsed laser deposition. The MBFO thin film was confirmed to be an epitaxial thin film having a (001) orientation crystal structure by Xray diffraction experiments. Compared to the BiFeO3 (BFO) thin film, the MBFO thin films have a shrunk a-axis lattice constant and a significantly elongated c-axis lattice constant, showing a c/a ratio of 1.15, and exhibiting high tetragonal strain. Due to the high tetragonal strain, the MBFO thin film exhibited higher polarization, magnetization, and d33 values than the BiFeO3 (BFO) thin film, resulting in enhanced multiferroic properties. From the results of the study on the relationship between the ferroelectric domain structure and the thickness observed by piezoresponse force microscope, it was confirmed that the domain wall energies of the MBFO thin films were larger than those of the BFO thin films. In addition, the I-V curves (photovoltaic current) showed that the MBFO thin films had the open-circuit voltages and photovoltaic currents higher than that of the BFO thin films due to its higher ferroelectric polarization and smaller band gap than those of the BFO thin films. Keywords Multiferroic properties . Mn doped BiFeO3 thin film . Tetragonally strained structure . Photovoltaic current
1 Introduction Lead-free ferroelectric materials such as SrBi2Ta2O9 and Bi3Ti4O12 have been widely investigated for the substitution of lead zirconate titanate (Pb(Zr,Ti)O3, PZT) materials because the PZT materials include the lead as a toxic element [1–3]. In particular, multiferroic materials such as BiFeO3 (BFO) are included in lead-free ferroelectric materials [4–13]. Interestingly, multiferroic thin films exhibit the ferroelectric property as well as the magnetic properties of ferromagnetism and anti-ferromagnetism depending on their thickness [4–13]. However, most multiferroic thin films have multiferroic characteristics at the temperature lower than room temperature because their magnetic properties are observed at the low temperature although they have ferroelectric properties at room temperature [4–13]. Hereupon, BFO thin films
* Hyun Wook Shin [email protected] * Jong Yeog Son [email protected] 1
Department of Applied Physics, Institute of Natural Sciences, Kyung Hee University, Yongin 446-701, South Korea
have been intensively investigated because BFO thin films are well known as room temperature multiferroic thin films [4]. For the magnetism, BFO thin films thicker than approximately 150 nm have anti-ferromagnetism but they have weak ferromagnetism when they are thinner than approximately 150 nm [14–16]. The BFO has a rhombic distortion central structure (space group R3c) and shows a G-type anti-ferromagnetic order w
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