二维磁性纳米结构材料的Monte Carlo模拟

运用MonteCarlo模拟方法,通过分析系统自旋序参数与温度的变化关系了解纳米结构材料磁性的特征.计算模拟结果表明,磁性纳米材料具有比同等大小和平均密度的单晶低的居里温度,且在相变过程中往往会出现一些亚稳态.研究结果提供了一种解析金属纳米结构材料特性的重要方法.

磁性纳米结构中由激光引起的超快自旋动力学研究

以单个磁性中心的NiO以及由Co和Ni等元素构成的双磁性中心的纳米结构为例,总结了近年所做的主要工作.为了在理论上实现磁性纳米结构中的超快自旋翻转和转移,提出了一种称为Λ进程(Λprocess)的超快自旋转换机理.在实际计算中,首先采用量子化学第一性原理计算得到磁性纳米结构中精确的隙间d电子态,然后考虑外加磁场和自旋轨道耦合分析磁性原子中的自旋局域化程度,最后引入激光脉冲项,研究在其作用下材料的自旋态经由Λ进程实现转换的时间历程.研究结果表明自旋翻转和转移可以在线偏振光的作用下在亚皮秒的时间尺度内完成.为了进一步实现对磁性分子自旋操控的检测和监控,采用附加于磁性中心上的CO分子对磁性分子进行标记.计算得到的与自旋态相关的C—O键振动频率表明自旋操控可以较容易地经由红外光谱实验间接监控.

磁性纳米结构的制备、表征、特性及应用

时纳米尺度的磁性物质结构的性质、制备及其在超高密度磁存储方面的应用等方面作了详尽的介绍。

Absorption performance of DMSA modified Fe_3O_4@SiO_2 core/shell magnetic nanocomposite for Pb^(2+) removal

The purpose of this study is to explore the adsorption performance of meso-2,3-dimercaptosuccinic acid(DMSA)modified Fe3O4@SiO2 magnetic nanocomposite(Fe3O4@SiO2@DMSA)for Pb2+ions removal from aqueous solutions.The effects of solution pH,initial concentration of Pb2+ions,contact time,and temperature on the amount of Pb2+adsorbed were investigated.Adsorption isotherms,adsorption kinetics,and thermodynamic analysis were also studied.The results showed that the maximum adsorption capacity of the Fe3O4@SiO2@DMSA composite is 50.5 mg/g at 298 K,which is higher than that of Fe3O4 and Fe3O4@SiO2 magnetic nanoparticles.The adsorption process agreed well with Langmuir adsorption isotherm models and pseudo second-order kinetics.The thermodynamic analysis revealed that the adsorption was spontaneous,endothermic and energetically driven in nature.

Electronic Resonant Splitting in a Nanostructure with Periodic Magnetic-Electric Barriers

In this letter, the transmission probability and the conductance of the ballistic electron are studied in a nanostructure with the periodic magnetic-electric barriers. We find that the resonant splitting increases with the number of periods increasing, so the number of the resonant peaks increases and the peaks become sharper. For the m-th periodic magnetic-electric barriers tunneling the splitting is （m - 1）-fold.

Magnetic and optical properties of zinc chromite nanostructures prepared by microwave method

The nanostructures of zinc chromite（Zn Cr2O4） were fabricated by the microwave method. It was shown that the well-crystallized spinel structure is formed after annealing at 700 °C. The influence of reaction time and irradiation power of oven on the size and shape of the as-prepared Zn Cr2O4 samples was studied. The synthesized samples were characterized by X-ray diffraction（XRD）, scanning electron microscopy（SEM）, energy dispersive X-ray（EDX）, transmission electron microscopy（TEM）, diffuse reflectance spectroscopy（DRS）, photoluminescence（PL） spectroscopy, Fourier transform infrared（FTIR） spectra and vibrating sample magnetometry（VSM）, respectively. The optical band gap calculated using DRS was found to be 3.50 e V for Zn Cr2O4 nanostructures. Photoluminescence measurements also confirmed this result.

The structure and properties of Fe_3O_4/P (NaUA-St-BA) magnetic composite nano particles

Fe3O4/P （NaUA-St-BA） core-shell composite micro spheres were in situ prepared by soapless polymerization of styrene and butyl acrylate, with Fe3O4magnetic colloidal particles coated with NaUA. The results of IR and XRD analysis demonstrated that the desired polymer chains have been covalently bonded to the surface of Fe3O4 nano particles. The morphology analysis by TEM confirmed that the composite particles have the core-shell structure and a relatively uniform diameter of about 100nm. The magnetic properties of the obtained composite latex particles were measured by VSM and found that they exhibited super paramagnetic properties. Finally, the prepared magnetic composite particles latex is stable for several months.

相互作用量子点的自旋相关输运

介绍了与磁性电极耦合的量子点的近藤共振、单电子能级自旋劈裂、磁化和线性电导等物理性质 .研究结果显示 ,当磁性电极磁矩取向相同的时候 ,线性电导在低温下呈现双峰结构 .而近藤共振和单电子能级的自旋劈裂都可以通过电极的内部磁化强度来控制 ,可以用来产生自旋阀效应 .

Formation mechanism and magnetic properties of three different hematite nanostructures synthesized by one-step hydrothermal procedure

The spindle-like, tubular, and tire-like hematite were successively fabricated by a facile, one-step hydrothermal procedure, which is of great importance in facilitating the controllable-synthesis process of commercial industrialization. A mechanism involving a formation-dissolution process was proposed based on the X-ray diffraction, scanning electron microscopy, trans-mission electron microscopy, and high-resolution transmission electron microscopy analysis. It was demonstrated that the presence of phosphate ions during the reaction process is crucial to the morphology evolution of hematite. Their different ad-sorption ability on the different crystallographic planes of hematite and a coordination effect with ferric ions could promote the preferential dissolution of the spindle-like hematite precursors along the long axis [001] from the tips down to the interior, and thus yield the tubular and tire-like hematite one by one with the increasing reaction time. The magnetic measurements have also been performed to investigate the different magnetic properties such as coercivity and low-temperature transition behavior of three different hematite nanostructures.

Rotating magnetic field-controlled fabrication of magnetic hydrogel with spatially disk-like microstructures

Composite biomaterials with controllable mi- crostructures play an increasingly important role in tissue engineering and regenerative medicine. Here, we report a magnetic hydrogel composite with disk-like microstructure fabricated by assembly of iron oxide nanopartides during the gelation process in the presence of rotating magnetic field. It should be mentioned that the iron oxide nanoparticles here were synthesized identically following techniques of Fer- umoxytol that is the only inorganic nanodrug approved by FDA for clinical applications. The microstructure of nano- particles inside the hydrogel was ordered three-dimensionally due to the twist of the aligned chains of magnetic nano- particles which leads to the lowest state of systematic energy. The size of microstructure can be tuned from several micro- meters to tens of micrometers by changing the assembly parameters. With the increase of microstructure size, the magnetothermal anisotropy was also augmented. This result confirmed that the assembly-induced anisotropy can occur even for the several micron aggregates of nanopartides. The rotating magnetic field-assisted technique is cost-effective, simple and flexible for the fabrication of composite hydrogel with ordered microstructure. We believe it will be favorable for the quick, green and intelligent fabrication of some com- posite materials.

Nanomagnetic CoPt truncated octahedrons:facile synthesis,superior electrocatalytic activity and stability for methanol oxidation

Nanomagnetic CoPt truncated octahedral nanoparticles （TONPs） were successfully synthesised through a facile one-pot strategy. These single crystal CoPt TONPs with an average size of about 8 nm exhibit excellent electrocatalytic performance of both activity and stability for methanol oxidation reaction （MOR）. The mass and specific activities of CoPt TONPs is 8 and 6 times higher than that of standard commercial Pt/C, respectively. After accelerated durability test （ADT）, the loss of electrochemical surface area （ECSA） for CoPt TONPs is only 18.5%, which is significantly less than that of commercial Pt/C （68.2%）, indicating that CoPt TONPs possess much better stability than commercial Pt/C in the prolonged operation. The Curie temperature of CoPt TONPs down to 8 nm is as high as 350 K with weak ferromagntism at room temperature （RT）, which is greatly valuable for recycling in the eletrocatalytic applications.

Magnetic yolk-shell structured anatase-based microspheres loaded with Au nanoparticles for heterogeneous catalysis

Magnetic yolk-shell structured anatase-based microspheres were fabricated through successive and facile sol-gel coating on magnetite particles, followed by annealing treatments. Upon loading with gold nanoparticles, the obtained functional magnetic microspheres as heterogeneous catalysts showed superior performance in catalyzing the epoxidation of styrene with extraordinary high conversion （89.5%） and selectivity （90.8%） towards styrene oxide. It is believed that the construction process of these fascinating materials features many implications for creating other functional nanocomposites.

Tuning crystal structure and magnetic property of dispersible FePt intermetallic nanoparticles

Dispersible FePt intermetallic nanopartides （NPs） with tunable composition were synthesized by thermal annealing of MgO coated A1-FePt （or A1-FePt-Fe304） NPs followed by an acid treatment to remove MgO. High-tem- perature annealing facilitates the conversion of FePt from disordered alloy to ordered intermetaUics. Under the protec- tion of MgO, the diffusion of Fe and Pt atoms was limited, making it possible for the atom reconstruction in the lattice to give discrete FePt intermetaUic NPs after a facile acid etching process. FePt intermetallic NPs formed face-centered cubic and face-centered tetragonal structures with their magnetic properties tuned by composition. The saturation magnetiza- tion was adjusted from 8 to 52 emu g^-1 by increasing the Fe concentration, while the coercivity reached a max/mum of 33 kOe when Fe concentration was 44%. After surface mod- ifications by hydrophilic or hydrophobic molecules containing thiol groups, FePt intermetallic NPs could be dissolved into water or hydrocarbon solvents. The hydrophilic L10-FePt in- termetallic NPs were applied as contrast agents for magnetic resonance imaging, showing a high transverse relaxivity of 328.6 mmo1^-1 L s^-l, which indicated the great potential of FePt intermetallic NPs as molecular probes for cancer diagnosis.

Laser generation of iron-doped silver nanotruffles with magnetic and plasmonic properties

A frontier topic in nanotechnology is the realization of multifunctional nanoparticles （NPs） via the appropriate combination of different elements of the periodic table. The coexistence of Fe and Ag in the same nanostructure, for instance, is interesting for nanophotonics, nanomedicine, and catalysis. However, alloying of Fe and Ag is inhibited for thermodynamic reasons. Here, we describe the synthesis of Fe-doped Ag NPs via laser ablation in liquid solution, bypassing thermodynamics constraints. These NPs have an innovative structure consisting of a scaffold of face-centered cubic metal Ag alternating with disordered Ag-Fe alloy domains, all arranged in a truffle-like morphology. The Fe-Ag NPs exhibit the plasmonic properties of Ag and the magnetic response of Fe-containing phases, and the surface of the Fe-Ag NPs can be functionalized in one step with thiolated molecules. Taking advantage of the multiple properties of Fe-Ag NPs, the magnetophoretic amplification of plasmonic properties is demonstrated with proof-of-concept surface-enhanced Raman scattering and photothermal heating experiments. The synthetic approach is of general applicability and virtually permits the preparation of a large variety of multi-element NPs in one step.

Recent developments of rare-earth-free hard-magnetic materials

Recent advances in rare-earth-free hard-magnetic materials including magnetic bulk, thin films, nanocomposites and nanostructures are introduced. Since the costs of the rare-earth metals boosts up the price of the high-performance rare-earth permanent magnets, there is a much revived interest in various types of hard-magnetic materials based on rare-earth-free compounds. The 3d transition metals and their alloys with large coercivity and high Curie temperatures(working temperatures) are expected to overcome the disadvantages of rare-earth magnets. Making rare-earth-free magnets with a large energy product to meet tomorrow's energy needs is still a challenge.