Synthesis of Superparamagnetic Magnesium Ferrite Nanoparticles by Microwave-Hydrothermal Method
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Synthesis of Superparamagnetic Magnesium Ferrite Nanoparticles by MicrowaveHydrothermal Method Seema Verma, Hari S. Potdar, Sadgopal K. Date and Pattayil A. Joy* Physical and Materials Chemistry Division, National Chemical Laboratory, Pune 411008, India ABSTRACT Superparamagnetic magnesium ferrite, MgFe2O4, nanoparticles were synthesized under mild microwave hydrothermal (MH) conditions. Transmission electron microscopic studies showed that the average particle size of the ferrite obtained is ~3 nm, with a narrow size distribution. Temperature dependent AC magnetic susceptibility measurements at 2 Oe showed characteristic feature of superparamagnetism with blocking temperature, TB, at 47 K. TB decreases with increasing DC magnetic field as evidenced by zero-field–cooled susceptibility studies at 50 and 500 Oe (TB = 38 and 27 K respectively). As a typical superparamagnetic behavior, the zero-fieldcooled and the field-cooled magnetizations diverge below TB. Magnetic hysteresis behavior is observed below TB, with a high coercivity of 185 Oe at 12 K, and magnetic hysteresis behavior disappears when measured above TB. The results indicate that MH method is highly suitable for the synthesis of superparamagnetic ferrite nanoparticles of uniform size distribution. INTRODUCTION Superparamagnetism is a unique and important feature of magnetism in magnetic nanoparticles. Current research interests in the study of the magnetic properties of ferrite nanoparticles are in terms of fundamental understanding as well as for technological and biomedical applications including high-density data storage, contrast enhancement of magnetic resonance imaging and magnetic carriers for site-specific drugs delivery [1,2]. Magnesium ferrite, MgFe2O4, is one of the important magnetic oxides with spinel structure. Apart from its applications in catalysis [3] and humidity sensors [4], superparamagnetic MgFe2O4 has been shown to be effective for achieving local hyperthermia [5]. Therefore, synthesis of nanosized superparamagnetic particles of magnesium ferrite, with narrow size distribution, and understanding the magnetic properties of the nanoparticles is important for fine tuning the particle nature and magnetic characteristics for many potential applications. For the synthesis of ferrites, chemically prepared precursors provide greater reactivity and therefore better homogeneity to the products due to the atomic level mixing of the constituent metal ions. Among the available solution chemistry based methods, hydrothermal method is an efficient and low-temperature method of synthesis of ceramic oxides, which is environmental friendly [6,7]. However, this method requires prolonged reaction time at low temperatures. The introduction of microwave energy into the chemical reaction leads to higher heating rates [8]. The microwave-assisted hydrothermal route of chemical synthesis is a rapidly developing area of research because it offers rapid heating, faster kinetics, homogeneity, higher yield, better reproducibility and is economical and ener
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