Magnetic properties of multicore magnetite nanoparticles prepared by glass crystallisation
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Magnetic properties of multicore magnetite nanoparticles prepared by glass crystallisation Christian Worsch • Markus Bu¨ttner • Peter Schaaf • Ruzha Harizanova • Christian Ru¨ssel Frank Schmidl • Paul Seidel
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Received: 28 June 2012 / Accepted: 2 November 2012 / Published online: 27 November 2012 Ó Springer Science+Business Media New York 2012
Abstract A glass with the composition 13K2O*13Al2O3* 16B2O3*43SiO2*15Fe2O3-x was melted and rapidly quenched in water. This leads to the formation of phase-separated droplets with diameters from 100 to 150 nm. Magnetite crystals with a size of 10–20 nm precipitate within these droplets. The magnetite containing phase-separated regions can be separated from the glass by dissolving the SiO2-rich amorphous glass matrix through boiling the pulverized glass in a concentrated aqueous sodium hydroxide solution. The residual, magnetite containing phase-separated droplets match multicore magnetite nanoparticles (McNP). The magnetite nanoparticles show superparamagnetic behaviour and as McNP, lead to a higher effective magnetic radius than single crystals. Magnetisation measurements of the McNP indicate that the particles show a narrow hysteresis, but the ratio of remanent to saturation magnetisation is not high enough for uniaxial anisotropy. The additionally performed
C. Worsch (&) C. Ru¨ssel Otto-Schott-Institut, Jena University, Fraunhoferstrasse 6, 07743 Jena, Germany e-mail: [email protected] C. Ru¨ssel e-mail: [email protected] M. Bu¨ttner F. Schmidl P. Seidel Institut fu¨r Festko¨rperphysik, Jena University, Helmholtzweg 5, 07743 Jena, Germany P. Schaaf Ilmenau University of Technologie, Gustav-Kirchhoff-Strasse 5, 98684 Ilmenau, Germany R. Harizanova University of Chemical Technology and Metallurgy, Kliment Ohridski Blvd. 8, 1756 Sofia, Bulgaria
temperature-dependent magnetorelaxometry (TMRX) measurements show peaks at 13 and 39 K in the distribution of the magnetic moment relaxation. The obtained interparticle distance of the magnetite within the McNP is smaller than 5 dC (core diameter), leading to strong magnetic interactions.
Introduction Magnetite is a magnetic mineral which naturally occurs in numerous geological formations [1]. Although magnetite has been a subject of scientific research for decades, some of its advanced properties are still not fully understood. The use of magnetite as a constituent of magnetic nanoparticles (MNP) allows a wide range of industrial, biological and medical applications. For example, stable colloidal liquids of MNP, called ferrofluids, are used in damping, bearing, sealing and lubrication, and as ink ingredients. They are also applied for magnetic fractionation, where the MNP are coated by organic agents and dispersed in an appropriate solution [2–6]. Among others, ferrofluids can be used in separation processes to remove micro-organisms from contaminated water. They are also a promising candidate for a large variety of biomedical applications [3, 7, 8] where the separation of tumour cells from human blood is used for c
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