Magnetic Iron Oxide Nanoparticles in 10−40 nm Range: Composition in Terms of Magnetite/Maghemite Ratio and Effect on the Magnetic Properties

Citations Over TimeTop 10% of 2011 papers

Abstract

Magnetic iron oxide nanoparticles in the 10−40 nm size range and with a reduced distribution in size have been synthesized under argon by using ammonium bases R4NOH (R = CH3, C2H5, C3H7) and a hydrothermal treatment. The size is tuned owing to the base to iron ratio and to the length of the alkyl chain R. We precipitate first ferric hydroxides at pH 1.5−2, then ferrous hydroxide at pH 5.5−6. The rapid increase of pH up to basic pH leads to the formation of magnetic iron oxide particles of 12 nm. For [base] to [Fe] ratio above 3.5, a homogeneous growth occurs during further hydrothermal treatment at 250 °C. The higher the quantity of base added and the longer the alkyl chain used, the smaller the particle size produced. For sizes above 20 nm, the Verwey transition at 120 K, characteristic of magnetite, is observed on the field cooling−zero field cooling magnetization curve. The nanoparticles can be described by a core−shell model, that is, a magnetite core surrounded by an oxidized layer close to maghemite. The fractional volume of maghemite increases as the particle size decreases so that below 20 nm, nanoparticles cannot be properly labeled as “magnetite”.

Related Papers

• → Influence of Nonstoichiometry and the Presence of Maghemite on the Mössbauer Spectrum of Magnetite(1995)90 cited
• → New insights into partial oxidation model of magnetites and thermal alteration of magnetic mineralogy of the Chinese loess in air(2004)52 cited
• → Oxidation Pathways in Bicomponent Ultrathin Iron Oxide Films(2012)47 cited
• → Studies on the oxidation of magnetite(1961)11 cited
• → Synthesis of iron oxide nanoparticles using precipitation method with different pH values(2021)2 cited