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Ferromagnetic and superparamagnetic ordered nanoparticles configurations
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Contract no: 71-119 / 2007
Contact: Dr. Ioan-Ovidiu Pana |
Results Stage I Stage II Stage III Stage IV Stage I
I. Synthesis procedures studies of FePt and Co Pt magnetic alloys. Chemical synthesis method. A mixture of oleic acid and oleyl amina was used for FePt nanoparticles synthesis, for colloidal stabilization and oxidizing prevention. The synthesis method is based on the reduction of Pt(acac)2 (acac = acetylacetonate, CH3COCHCOCH3) diol and the decomposition of Fe(CO)5 in solutions at high temperatures. The polyol synthesis procedure is based on using diol and poly-alcohols to reduce the metal salts to metal particles. The procedure was modified by using a long chain of 1,2-hexadecanediol for the reduction of Pt(acac)2 to Pt metal. The diameter and the composition of FePt nanoparticles can easily be controlled. The composition is adjusted by controlling the molar ratio of carbon/iron/Pt salt.
Coevaporation method The samples synthesis was done by coevaporation in electron beam with base pressure ~3*10-7 Pa. The evaporation sources are Pt, Fe and pure Al2O3. The substrate are fresh cuts of aCl (100) si MgO (100) crystals. During the deposition the substrates were kept at the temperature of 400o C. At first Pt was deposited with a speed of 0.1 nm/min, and later Fe was deposited with a speed of 0.4 nm/min on the Pt substrate. The thermal treatment of Al2O3/Fe/Pt films on NaCl and MgO substrates was made at the temperature of 600o C with different time lengths in a vaccum better than 2*10-5 Pa. The NaCl substrates were immersed in distilled water for removing the Al2O3/Pt or Al2O3/Fe/Pt films.
Results The TEM images of the as prepared Al2O3/Pt and Al2O3/Fe/Pt, evidenced the morphology of the Pt crystals and the FePt particles formed in island. As the density number of the FePt particles approached the Pt one, we concluded that the Fe crystal grows around the Pt particles.
II. Preliminary attempts for obtaining nanoparticles with narrow diameter distribution
Synthesis procedures Magnetic nanoparticles with core-shell structure, having a metallic core and noble metal shell, were obtained by inverse micelle method, using FeSO4 , HAuCl4, and K2PtCl6 as precursors, and NaBH4 as reducing agent. Cetil-trimetil-ammonium bromide (CTAB) was used as surfactant, and octane was used as reaction medium.
Diameter distribution study of the nanoparticles The nanoparticles were studied by TEM. We focused our attention on the core-shell magnetic nanoparticles La0.67Sr0.33MnO3@Au. The distribution curves were fitted with a lognormal equation. The dispersion factors were 0.15 and 0.14, indicating narrow diameter distribution.
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