Effect of cooling conditions on the magnetic structure of multiferroic BiFeO3 synthesized by mechanical activation
An attempt to synthesize multiferroic BiFeO3 by mechanical milling Bi2O3 and Fe2O3 powders showed very interesting results. 100 h milled powder was calcined at different temperatures and it was found that the BiFeO3 phase forms at 700°C followed by slow c
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riginally published in the journal Hyperfine Interactions, Volume 187, Nos 1–3, 1167–1172. DOI: 10.1007/s10751-008-9871-x © Springer Science + Business Media B.V. 2008
Abstract An attempt to synthesize multiferroic BiFeO3 by mechanical milling Bi2 O3 and Fe2 O3 powders showed very interesting results. 100 h milled powder was calcined at different temperatures and it was found that the BiFeO3 phase forms at 700◦ C followed by slow cooling. The magnetic behaviour and phase formation crucially depended on the cooling conditions. The samples were cooled from the calcinations temperature of 700◦ C in four different ways and Mössbauer measurements revealed different kinds of phases formed in these conditions. It was found that slow cooling favours BiFeO3 formation while rapid cooling leads to retention of Fe2 O3 . This was corroborated by differences in the magnetic ordering of phases as revealed by Mössbauer spectroscopy. Keywords Magnetic structure · Multiferroic BiFeO3 · Mechanical activation · Mössbauer spectroscopy
1 Introduction Recently, tremendous research interest is being shown in the multiferroic effect exhibiting coupling of charge, lattice, and spin orders, because of the underlying physics as well as potential applications in information storage [1]. The co-existence of ferroelectricity and ferromagnetism and their coupling with elasticity provide an
H. Thota · A. Garg (B) Department of Materials and Metallurgical Engineering, Indian Institute of Technology, Kanpur 208016, India e-mail: [email protected] B. Pandey · H. C. Verma Department of Physics, Indian Institute of Technology, Kanpur 208016, India H. C. Verma e-mail: [email protected]
N. S. Gajbhiye and S. K. Date, ICAME 2007. DOI: 10.1007/978-3-540-78696-2_160
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extra degree of freedom in the design of new functional sensors and multi-state memory devices [1–3]. Single-phase BiFeO3 (BFO), a multiferroic material, shows ferroelectric order below a high Curie temperature (TC ∼ 830◦ C) and antiferromagnetic order below the Néel temperature (TN ∼ 370◦ C). However, bulk BFO suffers from high leakage current (i.e., subject to dielectric breakdown at fields 99.9% purity, Sigma Aldrich) were milled in a high energy planetary ball mill using ball to powder ratio of 1:1 for a period of 100 h. This was followed by calcination at various temperatures up to 800◦ C for 1 h. Samples calcined at 700◦ C were cooled in four different ways: (a) sample quenched in water, (b) sample taken out of the furnace and cooled in air, (c) The furnace turned off with the sample inside and taken out after several hours, (d) similar to (c) but with O2 atmosphere provided in the furnace. X-ray diffraction (XRD) patterns were acquired using Siefert X-ray Diffractometer (Cu Kα λ = 1.54056 Å) operated at 30 kV and 20 mA. Mössbauer spectroscopic studies were made using 57 Fe as the source and standard transmission geometry. The data were analyzed using Lorentzian fits to six-line and two-line components using a least square routine.
3 Results and discussi
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