The copper (Cu) substitution in barium hexaferrite (BaFe12O19) crystals from the sol-gel auto-combustion synthesis is demonstrated as a cost-effective pathway to achieve alterable magnetic properties. Subsequent heat treatments at 450 °C and 1050 °C result in irregularly shaped nanoparticles characterized as the M-type BaFe12O19 with the secondary phase of hematite (α-Fe2O3). Despite the mixed phase, the substantial coercivity of 2626 Oe and magnetization as high as 74.8 emu/g are obtained in this undoped ferrite. The copper (Cu) doing strongly affects morphology and magnetic properties of BaFe12−xCuxO19 (x = 0.1, 0.3, and 0.5). The majority of particles become microrods for x = 0.1 and microplates in the case of x = 0.3 and 0.5. The coercivity and magnetization tend to reduce as Cu2+ increasingly substitutes Fe3+. From these findings, magnetic properties for various applications in microwave absorbers, recording media, electrodes, and permanent magnets can be tailored by the partial substitution in hexaferrite crystals.
Nanoparticles of 1-3 nm in radius were obtained from the reaction between Fe(acac) 3 and Pt(acac) 2 in the modified polyol process using two different solvents. The increase in surfactants (oleic acid and oleylamine) reduces the Fe:Pt ratio and increases the size of nanoparticles synthesized in dioctyl ether. In case of synthesis of benzyl ether, 2.5 mmol of each surfactants gave rise to uniform nanoparticles with hexagonal self-assembled pattern on a substrate whereas 5.0 mmol did not. Synchrotron small angle X-ray scattering profiles were fitted assuming a sphere form factor with a log-normal size distribution, using the least-squared minimization procedure. The average particle radii showed an increase with increasing surfactants from 2.5 to 5.0 mmol. The fitted log-normal size distributions also confirmed the effect of surfactant.
The synchrotron X-ray absorption technique was used to complement electron microscopy in the investigation of nanoparticles synthesized from the coreduction of iron acetylacetonate, Fe(acac)3and platinum acetylacetonate, Pt(acac)2. A much higher Pt composition than Fe leads to an extended X-ray absorption fine structure (EXAFS) spectrum for the sample that differs from that of fcc FePt nanoparticles. Most importantly, X-ray absorption near-edge structure (XANES) spectra clearly indicate the existence ofα-Fe2O3and Pt metal. Since these monodisperse nanoparticles have a diameter of around 4 nm and tend to self-assemble into hexagonal arrangements, they can be modeled as Pt-rich cores with anα-Fe2O3shell stabilized by organic surfactants.
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