| Superparamagnetic iron-gold nanoparticles were prepared by a reverse micelle method. The ferromagnetic iron formed a core of the nanoparticles while the diamagnetic gold a shell on the surface of the core. The presence of a gold coating inhibits oxidation and allows the particles to be stable. The Mössbauer spectra confirmed the superparamagnetic behaviour and indicated that the Fe and metallic Au exist as composite nanoparticles, not as separate particles. The obtained hyperfine parameters also confirmed the absence of iron oxides (Fe3O4, Fe2O3). Magnetic measurements in the temperature range of 4.2 280K show that the particles are superparamagnetic with a blocking temperature TB of 24K. At the temperature 280K (above TB) no coercivity HC is observed in the magnetization curve, while at 4.2K (below TB) coercivity HC is observed to be 150 Oe. |
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