Ferroelectric and ferromagnetic properties of Co doped BiFeO 3 thin films
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1256-N06-47
Ferroelectric and ferromagnetic properties of Co doped BiFeO3 thin films D. Barrionuevo1, S.P. Singh2, M. S. Tomar1#, R.S. Katiyar3 1
Department of Physics, University of Puerto Rico, Mayaguez, Puerto Rico, PR 00681 Department of engineering science and Materials, University of Puerto Rico, Mayaguez, PR 00681 3 Department of Physics, University of Puerto Rico, Rio Piedras, PR 00931 #Email: [email protected] 2
ABSTRACT Materials which possess electrical and magnetic coupling are of great interest for novel devices. Bi(Fe1-xCox)O3 (BFCO) material system was synthesized by solution route for various compositions and thin films were prepared by spin coating on Pt (Pt/Ti/SiO2/Si) substrates. Structural properties of the films were investigated by x-ray diffraction and Raman spectroscopy. X-ray diffraction patterns confirms intense (110) in BiFeO3 and Bi(Fe1-xCox)O3 with rhombohedra distorted perovskite structure without impure phase. Bi(Fe1-xCox)O3 films show week ferroelectric polarization and ferromagnetism at room temperature. Ferroelectric and ferromagnetic coupling could be attributed to the elimination of oxygen vacancies and increased stress in the crystal structure by partial replacement of Fe2+ ion by Co2+ ion. INTRODUCTION Multiferroics are the materials in which magnetism and ferroelectricity coexist. The search for these materials is driven by the prospect of controlling charge and spins by applied magnetic and electric fields. If ferroelectric and ferromagnetic ordering coexists, these materials are promising candidates for applications in memories, spintronics and magnetoelectric sensor devices [1-3]. Perovskite BiFeO3 (BFO) is ferroelectric (Tc ~1103 K) and antiferromagnetic (TN ~643 K), exhibiting weak magnetism at room temperature due to a residual moment from canted spin structure [4]. BFO is lead free material with low crystallization temperature of 550o C [5-6]. The lattice structure of a BFO crystal is a rhombohedrally distorted perovskite, which belongs to the space group R3c with unit cell parameters ar = 3.96Å and αr = 0.6◦ [7]. One of the problems of BFO thin films is low electrical resistivity which affects the measurement of ferroelectric/ferromagnetic properties at room temperature (RT). This high conductivity nature of BFO is attributed to the valence fluctuation of Fe ions (Fe3+ to Fe2+) and the volatile nature of Bi atoms [8-9]. However, due to slight difference in ionic radius of Fe2+ ion (0.087 nm) and Co2+ ion (0.082 nm), partial replacement of Fe2+ by Co2+ may distort the BFO lattice, and may effect the coupling parameters. We synthesized (110) oriented Co substituted BFO thin films which showed ferromagnetic and ferromagnetic coupling at room temperature. EXPERIMENTAL The precursor solution for the pure BiFeO3 samples was prepared by homogeneously mixing bismuth (III) nitrate pentahydrate and iron (III) nitrate nonahydrate with stoichiometric ratio
Bi/Fe 1:1 in 2-methoxy ethanol. The various concentrations of Co was incorporated by adding cobalt (II) nitrate to pr
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