Effect of octahedron tilt on the structure and magnetic properties of bismuth ferrite
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ISSN 2226-4108 CN 10-1154/TQ
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Effect of octahedron tilt on the structure and magnetic properties of bismuth ferrite Yang HONG, Jun LI*, Han BAI, Zhenjia SONG, Ming WANG, Zhongxiang ZHOU* School of Physics, Harbin Institute of Technology, Harbin 150001, China Received: April 22, 2020; Revised: May 31, 2020; Accepted: June 18, 2020 © The Author(s) 2020.
Abstract: Multiferroic BiFeO3-based ceramics were synthesized using the rapid liquid-phase sintering method. The rare-earth ion (Sm3+, Gd3+, Y3+) doping causes structural distortion without changing the intrinsic rhombohedral perovskite structure. Raman analysis shows that the effect of doping on E modes is greater than A1 modes, and the microstructure of FeO6 octahedron can be regulated by ion doping. A-site trivalent ion doped ceramics exhibit improved magnetism compared with pure BiFeO3 ceramic, which originated from the suppressed spiral spin structure of Fe ions. The tilt of FeO6 octahedron as a typical structure instability causes the anomalous change of the imaginary part of permittivity at high frequency, and doped ceramics exhibit natural resonance around 16–17 GHz. Keywords: bismuth ferrite (BiFeO3); magnetism; octahedron tilt; Raman spectrum; electromagnetic characteristics
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Introduction
Multiferroic materials are one of the most studied materials in recent years due to their unique properties, which exhibit more than two ferroic orders (such as ferroelectricity (TC), ferromagnetism (TN), ferroelastic, etc.). More than two orders can be coupled under certain conditions, exhibiting remarkable physical properties and excellent application potential [1–4]. Multiferroic materials are not only helpful for the applications but also provide a platform for exploring interesting effects like magnetoelectric effect, piezoelectric effect, etc. [5,6]. Among various known multiferroic materials, bismuth ferrite (BiFeO3, abbreviated as BFO) is a widely * Corresponding authors. E-mail: J. Li, [email protected]; Z. Zhou, [email protected]
investigated multiferroic material, in which TC ≈ 1100 K and TN ≈ 640 K coexist at room temperature [7,8]. The crystallographic structure of BFO is rhombohedral distorted perovskite structure with the space group R3c. The unit cell has a lattice parameter of a = 3.965 Å and a rhombohedral angle of ~89.3–89.48, and the oxygen octahedron is distorted with the minimum and the maximum O–O distances of 2.710 and 3.015 Å, respectively, and rotated by about 13.8 around the [111] axis [9]. BFO is classified as a G-type antiferromagnet below TN at the magnetic point of view; the combined action of exchange and spin–orbit interactions produce spin canting away from perfect antiferromagnetic ordering. The canted spin structure exhibits a space-modulated spiral structure (SMSS) with a period length of 62 nm, thereby resulting in a helimagnetic structure and a vanishing magnetization in the bulk [10,11]. The SMSS ordering in BFO is stable, and it persists when the temperature varies from 4 K to the Neel
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