Xiangcheng Sun

Synthesis, chemical ordering, and magnetic properties of FePtCu nanoparticle films

FePtCu nanoparticles with varying composition were prepared by the simultaneous polyol reduction of platinum acetylacetonate and copper bis(2,2,6,6-tetramethyl-3,5-heptanedionate) and the thermal decomposition of iron pentacarbonyl. As prepared the particles had a fcc structure with an average diameter of 3.5 nm and were superparamagnetic. Heat treatment of the self-assembled films at temperatures above 550 °C transformed the particles from the fcc to the L10 phase, give in-plane coercivities as high as 9000 Oe. X-ray diffraction revealed that the Cu remained in the films and the presence of an extra peak, indicating a second phase was present. Consistent with two or more phases, the magnetic hysteresis curves could be decomposed into a hard component (Hc>5000 Oe) and a soft component (Hc<2000 Oe). Unlike our earlier results for Ag in FePt, adding Cu to FePt did not lower the temperature required for phase transformation from the fcc to the L10 phase.

Synthesis and magnetic properties of CoPt nanoparticles

Magnetic nanoparticles CoPt were prepared by the chemical reduction of cobalt (II) chloride and chloroplatinic acid, then the samples were ultrasonicated for 2 h. After annealing at various temperatures from 400°C to 700°C for 1 h, the samples showed hard magnetic properties with coercivity up to 1.15 kOe at room temperature.

Magnetic and structural studies of the Verwey transition in Fe3−δO4 nanoparticles

Stoichiometric and cation-deficient magnetite Fe3−δO4 and γ-Fe2O3 particles have been prepared by the chemical method followed by heat treatments. The magnetic and structural properties were studied using neutron diffraction, magnetic measurements, and Mossbauer spectroscopy. Charge ordering of Fe3+ and Fe2+ and lattice distortion are not observed below the Verwey transition temperature in the stoichiometric and cation-deficient magnetite. It is found that the lattice parameter and the Verwey transition temperature decrease as the cation vacancy increases. The Verwey transition almost disappears in the Fe3−δO4 sample with δ=0.066. Mossbauer spectra show that the ratio of Fe3+/Fe2.5+ in stoichiometric magnetite can be modified by heat treatment. The Fe vacancies on the B sites change the nature of the Verwey transition. No cation vacancy ordering is observed for γ-Fe2O3, due to the small amount of cation vacancies in the compound.Stoichiometric and cation-deficient magnetite Fe3−δO4 and γ-Fe2O3 particles have been prepared by the chemical method followed by heat treatments. The magnetic and structural properties were studied using neutron diffraction, magnetic measurements, and Mossbauer spectroscopy. Charge ordering of Fe3+ and Fe2+ and lattice distortion are not observed below the Verwey transition temperature in the stoichiometric and cation-deficient magnetite. It is found that the lattice parameter and the Verwey transition temperature decrease as the cation vacancy increases. The Verwey transition almost disappears in the Fe3−δO4 sample with δ=0.066. Mossbauer spectra show that the ratio of Fe3+/Fe2.5+ in stoichiometric magnetite can be modified by heat treatment. The Fe vacancies on the B sites change the nature of the Verwey transition. No cation vacancy ordering is observed for γ-Fe2O3, due to the small amount of cation vacancies in the compound.

Synthesis and magnetic properties of monodisperse Fe3O4 nanoparticles

We report the high temperature reaction of iron acetylacetonate in phenyl ether in the presence of oleic acid and oleylamine that was used to synthesize monodisperse Fe3O4 nanoparticles. X-ray diffraction profile and high-angle annular dark-field images give evidence of self-assembled arrays with nanoparticle size of 4 nm. Magnetization versus temperature in the temperature range 2.5–160 K was measured in zero-field-cooled and field-cooled experiments and a blocking temperature Tb=20 K was obtained. Above Tb the nanoparticles show superparamagnetic behavior and the magnetization versus field for various temperature follows the Langevin function. M-H curves below Tb indicate the ferromagnetic behavior with Hc=60–400 Oe for temperature T=2.5–18.5 K.

Photoinduced electrooptics in the In2O3 nanocrystals incorporated into PMMA matrixes

We have observed an appearance of clear morphological structure in composites containing In2O3 nanocrystals (NCs) incorporated into polymethyl methacrylite (PMMA) matrices under optical treatment by a polarized femtosecond laser. The initial photoinduced treatment was carried out using a Ti:sapphire femtosecond laser emitting 140 fs p-polarized light at a maximum spectral wavelength 775 nm with pulse repetition 1 kHz. It was found that the average morphological radius is varied maximally only during illumination at liquid helium temperature (T = 4.2 K). The morphological average mean radius is strictly dependent on the sizes of incorporated In2O3 NCs. Afterwards we measured the linear electrooptic effect at cw He–Ne laser wavelength 633 nm during simultaneous treatment by 1060 and 530 nm coherent beams of a Nd–YAG picosecond laser. We have established that a decrease of the average morphological mean radius favours an increase of the optically poled linear electrooptic coefficient. The diameters of In2O3 NCs were evaluated using transmission electron microscopy (TEM) and light-scattering techniques, whereas the NC sizes and morphological average mean radius of formed nanocomposites were estimated by atomic force microscopy (AFM). A relationship between the diameter of the NC, composite morphological mean average radius and effective linear electrooptic coefficient was established. (Some figures in this article are in colour only in the electronic version)

Self-assembly of magnetic biofunctional nanoparticles

Spherical, ferromagnetic FePt nanoparticles with a particle size of 3 nm were prepared by the simultaneous polyol reduction of Fe(acac)3 and Pt(acac)2 in phenyl ether in the presence of oleic acid and oleylamine. The oleic acid ligands can be replaced with 11-mercaptoundecanoic acid, giving particles that can be dispersed in water. Both x-ray diffraction and transmission electron microscopy indicated that FePt particles were not affected by ligands replacement. Dispersions of the FePt particles with 11-mercaptoundecanoic acid ligands and ammonium counter ions gave self-assembled films consisting of highly ordered hexagonal arrays of particles.

Microstructure investigation on barrier shapes of double barrier magnetic tunnel junctions

Barrier shapes and its detailed microstructures in the double barrier magnetic tunnel junctions were intensively investigated by both high resolution transmission electron microscopy and electron holography. Two broad (>2nm) potential wells (i.e., shapes of AlOx layers) with slanted interfaces were observed in the electron hologram of the as-deposited samples. However, in the hologram of the annealed samples, two narrowed (down to 1.18nm) and almost equal (height) potential wells with sharp and steep interfaces were acquired. This indicates that the value of tunnel magnetoresistance can be increased from 12.8% to 29.4% at room temperature by annealing treatment where the sharpness and height of the barriers played a critical role.

Synthesis, Self-assembly and Magnetic Properties of FePtCu Nanoparticle Arrays

FePtCu nanoparticles with varying composition were synthesized by chemical solution-phase reduction of platinum and copper reagents and thermal decomposition of iron pentacarbonyl in the presence of oleic acid and oleyl amine stabilizers. As prepared the particles had fcc structure with an average diameter of 3.5 nm and were superparamagnetic. The particles were well dispersed in hydrocarbon solvents and could be self-assembled into two or three dimensions particles arrays with a variety of close-packing arrangements. Heat-treatment of the self-assembled films at temperatures above 550°C transformed the particles from the fcc to the L1 0 phase, giving in-plane coercivities as high as 9000 Oe. X-ray diffraction revealed that the Cu remained in the annealed FePtCu films and the presence of an extra peak, indicated a second phase was present. Consistent with one or more phases, the magnetic hysteresis curves could be decomposed into a hard component (H c > 5,000 Oe) and a soft component (H c 0 phase.

Microstructure Studies on Rutile TiO 2 -Sn Catalytic Particles

Instituto Mexicano del Petroleo (IMP), 07730, D.F. Mexico Novel physical and chemical properties of titania (TiO2, brookite, anatase and rutile) have made it an attractive material for multiples applications especially in catalysis [1, 2]. In particular, rutile type titania doped with specific elements had been synthesized by alternate approach, and also exhibited very good catalytic activities [3]. In this study, nanocrystals of rutile titania (TiO2) doped with tin (Sn) were successfully prepared by hydrothermal method. Titanium oxide type rutile was prepared from titanium (III) chloride solution at 15%, following the reported method in [4]. The reactive is placed in deionized water and maintained with a continuous stirring at room temperature and in contact with air over 60 hours. The precipitated obtained through the transformation of TiCl

Structure of Self-assembled Magnetic FePtCu Nanoparticles Arrays

In this study, a series of FexPtyCu100-x-y nanoparticles were chemically synthesized by solution-phase reduction of platinum and copper reagents and thermal decomposition of iron pentacarbonyl in the presence of stabilizers oleic acid and oleyl amine. As-prepared particles had a chemically disordered face-centered cubic (fcc) lattice with an average diameter of 3.5 nm. The particle size, and the corresponding size distribution were controlled by varying the organic surfactant (oleic acids, etc.), its concentration, and the reaction temperature. These particles were well dispersed in hydrocarbon solvents and self-assembled into two or three dimensions particles arrays with a variety of closepacking arrangements. Domain of monolayers, bilayers and multilayers of particles arrays were frequently detected in TEM specimens. Both cubic close-packed (ccp) and honeycomb arrays were also uniquely observed. It was also demonstrated that the controlled organic surfactant layer (organic capping) play a crucial role in determining assembly dimensions and symmetry as well as particle packing arrays.