Quasi-Hexagonal Ordered Arrays of FePt Nanoparticles Prepared by a Micellar Method

Hexagonally ordered arrays of magnetic FePt nanoparticles on Si substrates are prepared by a self assembly of diblock copolymer PS-b-P2VP in toluene, a dip coating process and finally plasma treatment. The as-treated FePt nanoparticles are covered by an oxide layer that can be removed by a 40 s Ar＋ sputtering. The effects of the sequence of adding salts on the composition distribution are revealed by x-ray photoelectron spectroscopy measurements. No particle agglomeration is observed after 600℃annealing for the present ordered array of FePt nanoparticles, which exhibits advantages in patterning FePt nanoparticles by a micellar method. Moreover, magnetic properties of the annealed FePt nanoparticles at room temperature are investigated by a vibrating sample magnetometer.     

Structural and Magnetic Properties of Fe-Doped Anatase TiO2 Films Annealed in Vacuum

Structural and magnetic properties of Fe-doped anatase TiO2 films fabricated by sol-gel spin coating are investigated. X-ray diffraction measurements reveal that Fe^3＋ ions are incorporated into the TiO2 lattice. No ferromagnetism-related secondary phases and magnetic nanopaxticles are observed in the films. The presence of electron paramagnetic resonance signals at 9- 2.0 supports oxygen vacancies and/or defects generated in the films after annealing in vacuum. Magnetic measurements indicate that Fe-doped anatase TiO2 films are ferromagnetic at room temperature. These observations suggest that oxygen vacancies and/or defects axe energetically favorable for the long range Fe^3＋-Fe^3＋ ferromagnetic coupling in Fe-doped anatase TiO2 films.     

Magnetic Properties and Nanostructures of FePtCu：C Thin Films with FePt Underlayers

Magnetic properties and nanostructures of FePtCu：C thin films with FePt underlayers （ULs） are studied. The effect of FePt ULs on the orlentation and magnetic properties of the thin films are investigated by adjusting FePt UL thicknesses from 2nm to 14nm. X-ray diffraction （XRD） scans reveal that the orientation of the films is dependent on FePt UL thickness. For a 5-nm FePtCu：C nanocomposite thin film with a 2-nm FePt UL, the coercivity is 6.S KOe, the correlation length is 59 nm, the desired face-centred-tetragonal （fct） ordered structure [Llo phase] is formed and the c axis normal to the film plane [（001） texture] is obtained. These results indicate that the beffer orientation and magnetic properties of the films can be tuned by decreasing the thockness of the FePt UL.     

Epitaxial Properties of Co-Doped ZnO Thin Films Grown by Plasma Assisted Molecular Beam Epitaxy

High quality Co-doped ZnO thin films are grown on single crystalline Al2O3（0001） and ZnO（0001） substrates by oxygen plasma assisted molecular beam epitaxy at a relatively lower substrate temperature of 450℃. The epitaxial conditions are examined with in-situ reflection high energy electron diffraction （RHEED） and ex-situ high resolution x-ray diffraction （HRXRD）. The epitaxial thin films are single crystal at film thickness smaller than 500nm and nominal concentration of Co dopant up to 20%. It is indicated that the Co cation is incorporated into the ZnO matrix as Co^2＋ substituting Zn^2＋ ions. Atomic force microscopy shows smooth surfaces with rms roughness of 1.9 nm. Room-temperature magnetization measurements reveal that the Co-doped ZnO thin films are ferromagnetic with Curie temperatures Tc above room temperature.     

Monolayer deposition of L10 FePt nanoparticles via electrospray route

The deposition monolayers of L1₀ FePt nanoparticles via an electrospraying method and the magnetic properties of the deposited film were studied. FePt nanoparticles in a size of around 2.5 nm in diameter, prepared by a liquid process, were used as a precursor. The size of the deposited particles can be controlled up to 35 nm by controlling the sprayed droplet size that is formed by adjusting the precursor concentration and the precursor flow rate. The droplets were heated in a tubular furnace at a temperature of up to 900 °C to remove all organic compounds and to transform the FePt particles from disordered face centered cubic to an ordered FCT phase. Finally, the particles were deposited in the form of a monolayer film on a silicon substrate by electrostatic force and characterized by scanning electron microscopy. The monolayer of particles was obtained by the high charge on particles obtained during the electrospraying process. The magnetic properties of the monolayer were investigated by magneto-optic Kerr effect measurements. Coercivity up to 650 Oe for a film consisting of 35 nm L1₀ FePt nanoparticles was observed after heat treatment at a temperature of 800 °C.     

Permanent Magnetic Properties of Melt-Spun YCo5Cx Ribbons

Ribbons of nominal compositions YCo5 Cx （x = 0, 0.2, 0.4, 0.6） are prepared by melt spinning at surface velocities v = 5, 10, 15, 20, 25, 30 and 35 m/s. YCo5 ribbon is crystallized in a single YCo5 phase of hexagonal CaCu5 structure. A small quantity of YCoC2 phase appears in the ribbons with C addition besides the YCo5 phase. With the increase of x the lattice constant c increases and a along with the unit cell volume decreases. The largest values of iHc = 888 kA/m and （BH）max = 58.4 k Jim3 at present for the YCo5 ribbon system were obtained with x = 0.4 and v = 20 m/s. The improvement of the permanent magnetic properties is rooted in the refinement of the microstructure and the appearance of the YCoC2 phase which can act as domain wall pinning centers.     

The influence of thermal annealing on the structural and magnetic properties of gold nanoparticles

In the past few years ferromagnetic-like behavior has been reported in metal gold nanoparticles coated with diverse organic surfactants. In this work we report on the effect of thermal annealing on the ferromagnetic-like behavior of oleic acid and oleylamine coated gold nanoparticles of about 7 nm size. The magnetic moment of the “as prepared” sample is about 3×10⁻² emu/g and the coercive field is 200 Oe at 10 kOe and 5 K, after the annealing the behavior changes from ferromagnetic-like to paramagnetic and the magnetization at 10 kOe decreases at a factor of 10. These results are compared with those obtained for oleylamine coated gold nanoparticles, which are diamagnetic at room temperature.     

Preparation and Luminescence Characteristics of Ca3Y2（BO3）4：Eu^3＋ Phosphor

Ca3Y2 （BO3）4：Eu^3＋ phosphor is synthesized by high temperature solid-state reaction method, and the Iuminescence characteristics are investigated. The emission spectrum exhibits two strong red emissions at 613 and 621 nm corresponding to the electric dipole ^5 Do- ^7F2 transition of Eu^3＋ under 365 nm excitation, the reason is that Eu^3＋ substituting for Y^3＋ occupies the non-centrosymmetric position in the crystal structure of Ca3 Y2 （BO3）4. The excitation spectrum for 613 nm indicates that the phosphor can be effectively excited by ultraviolet （UV） （254 nm, 365nm and 400nm） and blue （470nm） light. The effect of Eu^3＋ concentration on the emission intensity of Ca3 Y2 （BO3）4 ：Eu^3＋ phosphor is measured, the result shows that the emission intensities increase with increasing Eu^3＋ concentration, then decrease. The CIE colour coordinates of Ca3Y2 （BO3）4：Eu^3＋ phosphor is （0.639, 0.357） at 15mol% Eu^3＋.     

Fabrication of L10 FePtAg nanoparticles and a study of the effect of Ag during the annealing process

L1₀ ferromagnetic phase FePt nanoparticles containing Ag atoms (FePtAg) were synthesized by means of a liquid phase process, followed by annealing. The addition of Ag to FePt nanoparticles permits annealing to be conducted at a lower temperature (350 °C). This is further accompanied by a subsequent transformation in the crystal phase from the FCC superparamagnetic phase to the FCT (L1₀) ferromagnetic phase. The effects of annealing temperature and the Ag atoms inside the nanoparticles on the magnetic properties of the FePt nanoparticles have been studied. Using electron spectroscopy for the chemical analysis (ESCA), Ag atoms in the L1₀ phase FePtAg nanoparticles were found to be localized on the surface region of the annealed nanoparticles. The Ag atoms function to inhibit the oxidation of FePt, causing the particles to become more stable and to have ferromagnetic properties.     

Microstructure and magnetic properties of nanocomposite FePt/MgO and FePt/Ag films

An in-plane magnetic anisotropy of FePt film is obtained in the MgO 5 nm/FePt t nm/MgO 5 nm films (where t=5, 10 and 20 nm). Both the in-plane coercivity (H_c∥) and the perpendicular magnetic anisotropy of FePt films are increased when introducing an Ag-capped layer instead of MgO-capped layer. An in-plane coercivity is 3154 Oe for the MgO 5 nm/FePt 10 nm/MgO 5 nm film, and it can be increased to 4846 Oe as a 5 nm Ag-capped layer instead of MgO-capped layer. The transmission electron microscopy (TEM)-energy disperse spectrum (EDS) analysis shows that the Ag mainly distributed at the grain boundary of FePt, that leads the increase of the grain boundary energy, which will enhance coercivity and perpendicular magnetic anisotropy of FePt film.     

Microwave Magnetic Permeability of Fe3O4 Nanoparticles

Well-dispersed Fe3O4 nanoparticles are synthesized via an oxidization method with NANO2 as oxidant. The microwave magnetic properties of the composites are studied with different volume fractions of fe3O4 nanoparticles. It is found that a lower volume fraction corresponds to a higher magnetic resonance frequency. This could be ascribed to the enhancement of exchange interaction with a weakened dipolar interaction when the volume fraction decreases.     

Room-Temperature Ferromagnetism in Zn1-xMnxO Thin Films Deposited by Pulsed Laser Deposition

Zn1-xMnxO （x = O.Olq3.1） thin films with a Curie temperature above 300K are deposited on Al2O3 （0001） substrates by pulsed laser deposition. X-ray diffraction （XRD）, ultraviolet （UV）-visible transmission and Raman spectroscopy are employed to characterize the microstructural properties of these films. Room temperature ferromagnetism is observed by superconducting quantum interference device （SQUID）. The results indicate that Mn doping introduces the incorporation of Mn^2＋ ions into the ZnO host matrix and the insertion of Mn^2＋ ions increases the lattice defects, which is correlated with the ferromagnetism of the obtained films. The doping concentration is also proven to be a crucial factor for obtaining highly ferromagnetic Zn1-xMnxO films.     

Thermal treatment effects in the self-assembly of FePt nanoparticle arrays

This work concentrates on the influence of synthetic mechanisms of FePt nanoparticles on their self-arrangement and some structural and magnetic properties as studied by means of different electron microscopy techniques and SQUID magnetometry. High-reflux points associated with long boiling durations seem adequate to increase the iron precursor's decomposition yield and facilitate the simultaneous cubic to tetragonal FePt transformation, in single-phase FePt nanoparticles. Nevertheless, such conditions also result in the loss of long-range arrangement and in the appearance of coalescence effects. A core–shell structure comprising of FePt and Fe₃O₄ is favored under mild thermal conditions during synthesis, which seems to confront the undesirable atomic diffusion. Additionally, particle isolation due to the surfactant coating leads in an hcp-symmetry self-assembly. Moreover, working at lower temperatures allows a homogeneous mixture between different phases producing binary composite arrays.     

VUV/UV/X-Ray Excited Luminescent Properties of Eu^3＋ and Pr^3＋ Doped BiSbO4

Absorption spectra of BiSbO4 are studied. The electronic structure calculated by the DFT shows that BiSbO4 is a semiconductor, with direct band gap 2.96 eV, which is consistent with UV-visible diffuse reflectance experiment. The host lattice emission band is located at 440 nm under VUV excitation. Eu^3＋ and Pr^3＋ doped samples have high luminescence efficiency in emitting red and green light, respectively. From the partial density of states, Eu^3＋ doped emitting spectrum, and the host crystal structure parameters, the relationship between structure and optical properties is discussed. It is found that the Eu^3＋ ions occupied Bi^3＋ sites, and there could be an energy transfer from Bi^3＋ ions to RE^3＋ ions.     

High-Temperature Characteristics of Ti/Al/Ni/Au Ohmic Contacts to n-GaN

We present the high-temperature characteristics of Ti/Al/Ni/Au（15 nm/220 nm/40 nm/50 nm） multiplayer contacts to n-type GaN （Nd = 3.7 × 10^17 cm^-3, Nd = 3.0 × 10^18 cm^-3）. The contact resistivity increases with the measurement temperature. Furthermore, the increasing tendency is related to doping concentration. The higher the doped, the slower the contact resistivity with decreasing measurement temperature. Ti/Al/Ni/Au ohmic contact to heavy doping n-GaN takes on better high temperature reliability. According to the analyses of XRD and AES for the n-GaN/Ti/Al/Ni/Au, the Au atoms permeate through the Ni layer which is not thick enough into the AI layer even the Ti layer.     

氧化镍（绿镍矿）等温压缩及高压相变研究

 本文采用DAC（金刚石压砧高压腔）装置，对氧化镍进行了静水压、非静水压、电导率测量等系统高压实验，获取了氧化镍等温压缩、高压相变及电导率压力效应的新结果，并在实验数据的基础上，对其高压相变与电性及磁性变化关系及体弹性模量作了分析讨论。     

Decoration of carbon nanotube with size-controlled L10-FePt nanoparticles for storage media

In this work, first multi-wall carbon nanotubes (MWCNTs) with outer diameter about 20–30 nm are synthesized by a CVD method; they have been purified and functionalized with a two-step process. The approach consists of thermal oxidation and subsequent chemical oxidation. Then, monosize FePt nanoparticles along carbon nanotubes surface are synthesized by a Polyol process. The synthesized FePt nanoparticles are about 2.5 nm in size and they have superparamagnetic behavior with fcc structure. The CNTs surfaces as a substrate prevent the coalescence of particles during thermal annealing. Annealing at the temperature higher than 600 ^°C for 2 h under a reducing atmosphere (90 % Ar + 10 % H₂) leads to phase transition from fcc to fct-L1₀ structure. So, the magnetic behavior changes from the superparamagnetic to the ferromagnetic. Furthermore, after the phase transition, the FePt nanoparticles have finite size with an average of about 3.5 nm and the coercivity of particles reaches 5.1 kOe.     

Radial excitation states of η and η' in the chiral quark model

A chiral quark model is applied to calculate the spectra of pseudoscalar mesons η and η'. By analyzing the obtained spectra, we find that the mesons η'(2¹S₀), η(4¹S₀), η'(3¹S₀) and η'(4¹S₀) are the possible candidates of η(1760), X(1835), X(2120) and X(2370). The strong decay widths of these pseudoscalars to all the possible two-body decay channels are calculated within the framework of the ³P₀ model. Although the total width of η'(2¹S₀) is compatible with the BES Collaboration's experimental value for η(1760), the partial decay width to ωω is too small, which is not consistent with the BES result. If X(1835) is interpreted as η(4¹S₀), the total decay width is compatible with the experimental data, and the main decay modes will be mπ a₀(980) and m π a₀(1450), which needs to be checked experimentally. The assignment of X(2120) and X(2370) to η'(3¹S₀) and η'(4¹S₀) is disfavored in the present calculation because of the incompatibility of the decay widths.     

Multilayer Au/TiO2Composite Films with Ultrafast Third-Order Nonlinear Optical Properties

We report on the ultrafast third-order optical nonlinearity in multilayer Au/TiO2 composite films fabricated on quartz substrates by pulsed laser deposition technique. The linear optical properties of the films are determined and optical absorption peaks due to surface plasmon resonance of Au particles are observed at about 590hm. The third-order optical nonlinearities of the films are investigated by z-scan method using a femtosecond laser （50 fs） at the wavelength of 800 nm. The sample showed fast nonlinear optical responses with nonlinear absorption coefficient and nonlinear refractive index being -3.66 × 10^-10 m/W and -2.95 × 10^-17 m^2/W, respectively. The results also show that the nonlinear optical effects increase with the increasing Au concentration in the composite films.     

Superparamagnetic FePt nanoparticles as excellent MRI contrast agents

Chemically disordered face-centered cubic (fcc) FePt nanoparticles (NPs) with a mean diameter of 9 nm were synthesized via pyrolysis of iron(III) ethoxide and platinum(II) acetylacetonate. The surface ligands of these NPs were then exchanged from oleic acid to tetramethylammonium hydroxide (TMAOH) to measure the longitudinal (T₁) and transverse (T₂) proton relaxation times of aqueous dispersion of FePt NPs. Magnetic resonance relaxometry reveals that TMAOH-capped FePt NPs have a higher T₂-shortening effect than conventional superparamagnetic iron oxide NPs, indicating that fcc-phase FePt NPs might be superior negative contrast agents for magnetic resonance imaging.