Synthesis and Magnetic Properties of Cobalt Ferrite Nanoparticles
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Synthesis and Magnetic Properties of Cobalt Ferrite Nanoparticles Morad F. Etier1, Vladimir V. Shvartsman1, Frank Stromberg2, Joachim Landers2, Heiko Wende2, Doru C. Lupascu1 1 Institute for Materials Science, University of Duisburg-Essen, Essen, Germany 2 Experimental Physics, Faculty of Physics, University of Duisburg-Essen, Duisburg, Germany ABSTRACT Nanopowders of cobalt iron oxide (CoFe2O4) were successfully fabricated by the coprecipitation method followed by a technique to prevent particle agglomeration. Particle sizes were in the range of 24 to 44 nm. The size of cobalt iron oxide particles decreases with increasing the concentration of the precipitation agent. The crystal structure was confirmed by Xray diffraction (XRD), the chemical composition by energy dispersive spectroscopy (EDS), and phase changes by thermogravimetric differential thermal analysis (TGA-TDA). The particle morphology was analyzed by scanning electron microscopy (SEM). Magnetic properties were investigated by SQUID magnetometry and Mössbauer spectroscopy. Being nearly monodisperse and non-agglomerated the prepared cobalt iron oxide powders are the base for synthesizing magnetoelectric composites embedded in a ferroelectric BaTiO3 matrix. INTRODUCTION Cobalt iron oxide, CoFe2O4, is one of the most widely used materials in magnetic recording due to its high coercivity (about 5400 Oe), moderate magnetization (84 emu/g), and good chemical stability. Cobalt iron oxide also exhibits high hardness, wear resistance, electrical insulation, high cubic magnetocrystalline anisotropy, high electromagnetic performance, and photomagnetism [1-3]. CoFe2O4 is a member of the inverse spinel structure family where the Co+2 ions occupy half of the octahedral coordination sites. Fe+3 cations occupy the other half of the octahedral sites as well as the tetrahedral sites. Below TC = 820 K [2] CoFe2O4 is in a ferrimagnetic state, where the magnetic moments from the Fe+3 ions partly cancel each another. The net contribution to magnetization is reduced [4]. The magnetic properties of cobalt iron oxide nanoparticles mainly depend on the annealing temperature. For increasing annealing temperature the particle size rises and the saturation magnetization and the coercive field increase [5]. Large magnetostriction makes CoFe2O4 promising for fabrication of composite multiferroics [6]. In these materials the magnetoelectric (ME) effect, i.e. change of the polarization under an external magnetic field, is engineered between the order parameters of piezoelectric and magnetostrictive constituents [7]. An external electric field applied to the composite will induce a mechanical strain in the piezoelectric constituent transferred to the magnetostrictive component at the respective interfaces, where it induces a change of magnetization. Analogously, an applied magnetic field results in a change of the polarization in the piezoelectric constituent. An enhanced ME coupling is expected in composites with relatively large, well-defined interface areas. This is the case, e.g., in
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