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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 II - Superparamagnetic nanoparticles assemble of Ni and Co and also core-shell types with narrow dimensional distribution were obtained. The synthesis of transition-metal nanoparticles is based on the reduction of their salts in aqueous or non- aqueous systems. The Co nanoparticles were obtained by inverse micelle method, using CoCl2 and NaBH4 1M, within the reaction Co2+ was reduced to Co0 . - Compositional characterization of the composite nanoparticles was performed by ICP-AES and XPS techniques. - It has been evidenced the doublets resulted from spin-orbit coupling of p , d and f orbitals. For Mn3d it has been shown the existence of two oxidation states corresponding to Mn3+ and Mn4+ . La have 4 components and O have 2 components corresponding to the two oxidation state of Mn. - In the case of Au atoms it was shown the existence of two chemical states. We consider that the two states correspond to the Au atoms situated in the shell and in the Au/LSMO interface. - The existence of the core-shell structure was observed on both systems Fe@Au and LSMO@Au by using XPS with controlled sputtering with Ar ions. - The morphology and structure of the nanoparticles was investigated by TEM and XRD. - From the line shape analysis of the XRD peaks of the Fe@Au system, the mean diameter of Au nanocrystallites were calculated <DAu>1= 24.5 nm, <DAu>2= 22.1 nm, and <DAu>3= 24.8 nm, corresponding to FA1, FA2 and FA3 samples. The mean diameters of the Fe core corresponding to the three samples analyzed was calculated in the same way <DFe>1 = 14.6 nm, <DFe>2 = 12.0 nm, and <DFe>3 = 15.1 nm. In accordance with the core-shell type the calculated values of Fe are smaller than the values of Au. - The size distribution was obtained by analyzing the TEM images for at least 400 nanoparticles for each of the samples. The normalized distribution of the diameters is well fitted by lognorm distribution function. - It was shown that the majority of atoms are in the large diameter nanoparticles. This remark explains the high values of the calculated nanocrystallites diameters obtained XRD line profile analysis, compared to the mean diameters observed by TEM. - From the analysis of the volume fraction distributions it resulted that the nanoparticles having small diameters are more numerous than those having big diameters. Even though the majority of atoms are in nanoparticles with big diameters, the superparamagnetic behavior of the system is determined by the nanoparticles with small diameter. - The XRD line profile analysis of the LSMO@Au was performed on the most intens lines (110) 2θ = 32.63 and (310) 2θ = 77.9 partially superimposed with Au (311) la 2θ = 77.54. By comparing the LSMO@Au and LSMO difractograms it was determined the modifications produced by Au coating. - The correlation between the magnetic properties of the superparamagnetic nanoparticles with the diameter and narrows size distribution was determined. - The magnetization measurements were performed by VSM technique at room temperature for the Fe@Au samples. - The mean magnetic diameter D0(m) , dispersion of size distribution s(m), and saturation magnetization MS were calculated by fitting the magnetization curves. - From the analysis of FC and ZFC curves it was obtained TRM curve. By using the magnetic volumes Vm resulted from M(H) cureves fitting it was obtained the effective anisotropy constant Keff . - The modifications induced by the narrowing of the size distributions upon the optical properties was investigated for nanoparticles covered with different thickness of Au. - It was investigated the dependence of the plasmon resonance frequency with the Au concentration (the thickness of the Au shell of the LSMO@Au nanoparticles). I was shown that the if the Au concentration is smaller and the size distribution are narrower the shift of the maxim of the Plasmon resonance frequency is bigger. - Superparamagnetic nanostructures in porous alumina matrix were obtained. - Wetting based methods, Precursor film infiltration methods and Solution wetting methods were tested. - Morphological, structural and magnetically characterization of the superparamagnetic nanoparticles in porous alumina matrix structures was carried out. - Three sets of heterocomposite samples were prepared consisting in polystyrene nanotubes which contain LSMO@Au nanoparticles inside the walls with nanoparticles concentration of 20% , 30% and 40% volume percents named PS-LSMO1, PS-LSMA2 and PS-LSMA3. By XPS elemental analysis it was certified that the LSMO@Au nanoparticles were uniformly dispersed in the nanotubes. - Hard ferromagnetic nanoparticles based on FePt and CoPt alloys were obtained. For the magnetic measurements of the obtained samples the VSM technique was used. |
