Abstract
The synthesis of FePt nanocrystals is typically performed in an organic solvent at rather high temperatures, demanding the addition of the in situ stabilizers oleic acid and oleylamine to produce monomodal particles with well-defined morphologies. Replacing frequently-used solvents with organic media bearing functional moieties, the use of the stabilizers can be completely circumvented. In addition, various morphologies and sizes of the nanocrystals can be achieved by the choice of organic solvent. The kinetics of particle growth and the change in the magnetic behavior of the superparamagnetic FePt nanocrystals during the synthesis with a set of different solvents, as well as the resulting morphologies and stoichiometries of the nanoparticles were determined by powder X-ray diffraction (PXRD), small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), inductively coupled plasma optical emission spectroscopy (ICP-OES)/mass spectrometry (ICP-MS), and superconducting quantum interference device (SQUID) measurements. Furthermore, annealing of the as-prepared FePt nanoparticles led to the ordered L10 phase and, thus, to hard magnetic materials with varying saturation magnetizations and magnetic coercivities.
Highlights
Iron platinum (FePt) nanoparticles gained high scientific interest due to their large uniaxial magnetocrystalline anisotropy [1,2,3], high saturation magnetization and coercivity [4,5,6,7], as well as good chemical stability [1,8]
Three alternative non-aqueous sol-gel synthesis routes for the generation of superparamagnetic fcc-FePt nanocrystals with varying particle sizes and high saturation magnetization were tested without the addition of any in situ stabilizers using the solvents triethylene glycol, benzyl alcohol, and benzylamine, as well as the non-toxic molecular precursors iron(III) and platinum(II) acetylacetonate (Figure 2)
Each route resulted in highly-uniform nanocrystals that could be stabilized individually, with the exception of the BnNH2 system, which resulted in small agglomerates
Summary
Iron platinum (FePt) nanoparticles gained high scientific interest due to their large uniaxial magnetocrystalline anisotropy [1,2,3], high saturation magnetization and coercivity [4,5,6,7], as well as good chemical stability [1,8]. Those characteristics are promising with regard to potential applications, such as magnetic hyperthermia [4,9,10], biomedical imaging [11,12], ultrahigh density magnetic recording [13,14,15,16,17], or advanced permanent magnets [18,19,20,21]. Higher variations in the Fe:Pt ratio result in the ordered L12 phases of FePt3, Fe3Pt or mixtures of all three crystal structures [23]
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