In the present work, we have synthesized and characterized magnetic nanoparticles of maghemite γ-Fe2O3 to study their structural and magnetic properties. For the preparation, magnetite precursor, were oxidized by adjusting the pH = 3.5 at about 80 °C in an acid medium, The mean size of the maghemite particles calculated from the X-ray diffractogram was around 5.7 nm. Mössbauer spectroscopy measurements at room temperature show their superparamagnetic behavior. Furhermore, Mössbauer measurements were carried out at 77 K and 4.2 K in order to find the typical hyperfine fields of the maghemite. Magnetite phase was not found. FC and ZFC magnetization curves measured at 500 Oe indicate a blocking temperature of 105.3 K. The magnetization measurements also show almost zero coercivity at RT. TEM images show nanoparticles with diameter smaller than 10 nm, which are in good agreement with the X-ray pattern and the fitting of the magnetization data.
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Acknowledgements We are indebted to Dr. F. E. Wagner from the Physics Department of the Technical University of Munich, 85747 Garching, Germany for carrying out the Mössbauer measurements at 4.2 K and Dr. J. Coaquira and L. León from the Universidade de Brasilia for carrying out the Mössbauer measurements at 77 K. The work in Cambridge was supported by a grant from the Engineering and Physical Science Research Council (EPSRC).
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- Blocking temperature
- Mössbauer spectroscopy