晶粒尺寸分布对纳米永磁材料矫顽力的影响

采用对数高斯分布模型,研究了晶粒尺寸分布对纳米硬磁材料有效各向异性Keff和矫顽力Hc的影响.研究结果表明:Keff和Hc随晶粒尺寸分布的集中而增加.纳米硬磁材料矫顽力的下降主要是由有效各向异性的下降引起的.为获得较高的矫顽力,晶粒尺寸分布应尽可能的集中.     

Fe含量对FePt磁性薄膜的微结构和磁特性的影响

用直流磁控溅射方法和原位退火工艺在玻璃基片上制备了FexPt100-x纳米颗粒膜.研究发现,Fe含量对FePt纳米颗粒膜的微结构和磁特性有很大的影响.矫顽力随Fe含量的增加而增大,当x=48时矫顽力Hc达到了1 040 kA/m,样品出现很好的有序化L10结构扫描探针显微镜(SPM)观察结果显示,所有样品具有横跨数个晶粒的粒状磁畴,Fe48Pt52的粗糙度Ra大约0.6 nm.     

FePt纳米颗粒的制备与表征

通过化学还原法制备FePt纳米颗粒,研究热处理前后其磁性能的变化.XRD及TEM分析表明,所制备的FePt纳米颗粒为fcc结构,颗粒为类球形且分散性较好,尺寸约为5.0 nm,热处理使FePt纳米颗粒从无序的fcc相变成有序的fct结构.VSM显示所制备FePt纳米颗粒的矫顽力为零,呈现超顺磁性,500 ℃高温退火处理后矫顽力可达1/(2π)×106 A/m.     

钴铁氧体复合纳米颗粒的制备及其磁性

通过溶胶凝胶法制备尖晶石CoFe2O4/α-Fe复合纳米颗粒体系,用X射线衍射仪、振动样品磁强计对样品的结构和磁性进行了研究.这种新型材料具有较高的饱和磁化强度Ms(51.44 A.m2/kg)和矫顽力Hc(10.8×104 A/m),最大磁能积(BHmax)相比同样方法制备的纯CoFe2O4有较大的提高.磁性能的改善可能来源于处于内层的CoFe2O4与外壳层的α-Fe之间的交换耦合作用.     

纳米Fe_3O_4颗粒的制备及磁性能

采用X-ray衍射、高能X-ray衍射、透射电子显微镜及振动样品磁量计等表征手段,研究了不同制备工艺对Fe3O4纳米粒子的平均晶粒尺寸及磁性能的影响.结果表明多元醇方法所制备的Fe3O4粉体平均粒径为32 nm,其饱和磁化强度为6.8×10-3A/m(该值比块体Fe3O4的饱和磁化强度约降低了8%),剩磁Mr=4.2×10-3A/m,矫顽力Hc=1.43×10-2T;通过共沉淀方法得到的Fe3O4粉体平均粒径显著减小为7 nm,但是其饱和磁化强度也明显降低为3.3×10-4A/m,比块体Fe3O4的饱和磁化强度减小约96%,剩磁及矫顽力也下降为零.这是由于小尺寸效应导致出现超顺磁现象,说明Fe...     

Fe-Al_2O_3纳米颗粒膜的巨磁电阻效应及微结构

采用磁控溅射方法在玻璃基片上制备了一系列的 Fe- Al2 O3 颗粒膜样品 ,对样品的巨磁电阻效应 (GMR)和磁性能进行了测量 ,并用高分辨电镜 (HRTEM)对膜中 Fe颗粒的微结构进行观察 .结果表明 :磁电阻 MR随 Fe含量而变化 ,在体积分数为 47%时获得最大值 4.0 % .45 % Fe-Al2 O3 颗粒膜的室温磁性表现为超顺磁性 ,磁电阻 MR与 - (M/Ms) 2 成正比 ,相关常数 A≈ 0 .0 3 6 .HRTEM观察表明 ,当 Fe颗粒尺寸约小于 1 nm时 ,Fe颗粒为非晶态 ,而大于该尺寸时则为晶态 .在 Fe- Al2 O3 颗粒膜体系中存在与隧道相关的 GMR,GMR的起因可归于传输电子的自旋相关的散射     

纳米晶Ni_(1-x)Zn_xFe_2O_4铁氧体的水热合成与磁性能

采用水热法在180℃下合成纳米级的尖晶石相NiZn铁氧体,使用Χ射线衍射(XRD)、红外光谱(FTIR)、高分辨透射电镜(HRTEM)和振动样品磁强计(VSM)分别表征NiZn铁氧体纳米粉体的相组成、微结构以及磁性能.XRD衍射谱和红外光谱(FTIR)表明180℃合成的纳米晶NiZn铁氧体为单一尖晶石相;高分辨透射电镜照片分析表明Ni0.6Zn0.4Fe2O4颗粒为立方片状,颗粒均匀,尺寸在20nm左右,晶格结构完整,面间距0.44nm.Ni0.6Zn0.4Fe2O4铁氧体的饱和磁化强度(Ms)和矫顽力(Hc)分别为11.9emu·g-1和93.5Oe,NiZn铁氧体的矫顽力随着Zn2+含量的增加而减小,此为A位和B位磁性离子间超交换作用下降所致.     

三维晶粒尺寸及分布对纳米永磁材料磁性能的影响

本文建立厚度为d的晶粒间界相均匀包围边长为D的三维立方体模型.假定晶粒间界相削弱了晶粒间的交换耦合相互作用.研究了晶粒尺寸及分布对纳米永磁材料有效各向异性及矫顽力的影响.结果表明：单个晶粒的平均各向异性随晶粒尺寸D的增大而增大.且材料的有效各向异性Keff和矫顽力Hc均随平均晶粒尺寸的增大而上升,而上升速率逐渐减慢.Keff和Hc随分布系数的增加而下降,且下降速率逐渐减慢.当Pc=0.7,=1.5,K1（0）=0.2Kh,d=2nm时,我们计算的矫顽力与实验数值符合地很好（Pc是无量纲因子,在0到1之间取值.Kh是晶粒内部正常的磁晶各向异性常数,K1（0）和d分别为晶粒间界相的各向异性常数和厚度）.     

甘氨酸燃烧法制备纳米晶CoFe_2O_4铁氧体及烧结温度对其磁性能的影响

利用甘氨酸作为燃料和配合剂, 采用自蔓延燃烧法制备纳米晶钴铁氧体, 并通过X射线衍射、扫描电子显微镜和振动样品磁强计表征样品的结构和磁性能. 结果表明, 平均晶粒尺寸对样品的磁性能影响较大, 晶粒尺寸随烧结温度的变化而变化, 并得到了矫顽力Hc和比饱和磁化强度σs随烧结温度的变化曲线.     

铁纳米颗粒的脉冲激光气相蒸发-液相合成研究

采用激光气相蒸发-液相收集新方法合成纳米Fe颗粒,主要利用扫描电镜、透射电镜和振动样品磁强计等分析方法对纳米颗粒的形貌、大小、磁性及合成机理进行了分析.结果表明:以45#钢为靶材、20%乙二醇+80%乙醇为液相收集体系和N2为载气,在激光能量密度为42 J/mm2、脉宽3 ms、频率10 Hz和N2流量为0.5 L/min的条件下,成功制备出了Fe纳米颗粒;颗粒呈球形且呈链状连接趋势,主要粒径在20~30nm之间;纳米铁颗粒矫顽力为523 Oe,饱和磁化强度为45 emu/g;脉冲激光诱导45#钢靶材产生含Fe成分的等离子体,在气相中均匀成核,并发生一定程度的长大,然后在载气N2的带动下进入液...     

Restricted allowable generalized quantum gates

An allowable generalized quantum gate (introduced by Long, Liu and Wang) has the form of U = Σ _k=0 ^d−1 c _k U _k , where U _k’s are unitary operators on a Hilbert space H and |Σ _k=0 ^d−1 c _k |⩽1 and |c _k |⩽1 (0⩽k⩽d−1). In this work we consider a kind of AGQGs, called restricted allowable generalized quantum gates (RAGQGs), satisfying 0 < Σ _k=0 ^d−1|c _k |⩽1. Some properties of the set RAGQG(H) of all RAGQGs on H are established. Especially, we prove that the extreme points of RAGQG(H) are exactly unitary operators on H and that B(H)=R ⁺ RAGQG(H).     

γ′-Fe4N纳米晶薄膜的结构及低温磁性

采用直流磁控溅射方法, 在Si(100)单晶衬底上制备γ′-Fe₄N纳米晶薄膜样品, 并利用X射线衍射(XRD)和振动样品磁强计(VSM)对样品的结构和磁性进行测试分析, 给出了比饱和磁化强度及矫顽力与温度的关系. 结果表明, 样品沿(111)晶面择优生长, 具有单一的易磁化方向, 且易磁化方向平行于（111）晶面. 随着测量温度的降低, γ′-Fe₄N纳米晶薄膜样品的比饱和磁化强度σ_s增加, 矫顽力H_c增大, 剩磁比σ_r/σ_s减小. 通过理论拟合确定了比饱和磁化强度与矫顽力随温度的变化关系, 矫顽力随温度的变化满足T^1/2规律, 比饱和磁化强度σ_s与温度不满足Bloch的T^3/2规律, 表明在80~350 K温度范围内自旋波之间存在较强的相互作用.      

磁性纳米颗粒系统的铁磁共振和共振线宽分析

 对非相互作用磁性纳米颗粒系统的FMR线型模型进行了研究,以铁磁体从应用场中获得自由能F为例,导出磁性颗粒在较小各向异性时,共振场H_r与有效各向异性场H_A^eff的关系,这个结果与Raikher和Stepanou的结果一致.继而还对共振场线宽进行了分析,并与Smit和Beljers模型进行了比较,其结论说明:在超顺磁区域有效各向异性场H_A^eff对塞曼(Zeeman)相互作用和附加应用场H是不确定的.尤其是这种情况在H_A^eff较小、高温(高温区域),且H_A^eff≈H时,变得更显著.为此提出了随机颗粒阵列及参数特征对这个结果的影响机制.     

Analysis of active sites for N2 and H^＋ reduction on FeMo-cofactor of nitrogenase

Dinitrogen (N2) and proton (H ),which act as physiological substrates of nitrogenase,are reduced on FeMo-co of the MoFe protein. However,researchers have different opinions about their exact reduction sites. Nitrogenases were purified from the wild type (WT) and five mutants of Azotobacter vinelandii (Av),including Qα191K,Hα195Q,nifV-,Qα191K/nifV- and Hα195Q/nifV-; and the activities of these en-zymes for N2 and H reduction were analyzed. Our results suggest that the Fe2 and Fe6,atoms closed to the central sulfur atom (S2B) within FeMo-co,are sites for N2 binding and reduction and the Mo atom of FeMo-co is the site for H reduction. Combining these data with further bioinformatical analysis,we propose that two parallel electron channels may exist between the 8Fe7S cluster and FeMo-co.     

Limit of Julia sets forz d +c

The limit behavior of Julia set J(fd,c) for polynomials fd,c(z) = zd + c is considered. That { J( fd,c) } d≥2 converges to the unit circle S1 in Hausdorff metric for some fixed parameter c is proved and some examples showing { J( fd,C) } d≥2 has no limit are given.     

QSPR between Physical-Chemical Properties and Molecule Parameters of Alkanes

A set of molecule parameters, namely, N, N′, p, q, n, were used to express the structures of alkanes. A correlative model was established between certain physical-chemical properties and molecular parameters of alkanes by regression method. Eight physical-chemical properties, such as evaporation heat （△vHm^20）, density（D^20 ）, capacity （C^20）, surface tension （δ^20）, boiling point （Tb）, critical temperature（Tc）, critical pressure（Pc） and critical volume（Vc）, of fifty-six C3-C16 alkanes were calculated directly from the model in this paper. The calculated values are in good accordance with the literature ones reported for alkanes, and the correlation coefficients （R） equal or exceed 0.99 . The research results indicate that the principle of the method is simple and clear, the method is practical, the correlativity is excellent, and the predicted data are credible.     

Thermodynamic characterization of two novel spin-crossover complexes

Spin-crossover complexes are of great interest to the scientists because of their potential application in molecular-based electronic devices. Some octahedral metal compounds with 3dn (4 ≤ n ≤ 7) configuration can induce a spin state conversion through a fine tuning condition (temperature, pressure, light irradiation, etc.). If the conversion occurs reversibly with a hystersis loop and color change, it will make the system possessing memory effect. The memory effect can be magnified and the …     

Treatment of Wastewater Containing Polyacrylamide Using Three Dimensional Electrodes

A method using three-dimensional electrode is applied to treat wastewater in oil fields, which contains polyacrylamide (PAM), for analogue. A best condition for electrolysis (I=1.0 A, t=90 min, c=0.1%, m=980 g,φ =5 mm, d=5.0 cm) has been determined, under which the COD removal efficiency reached 96.0%, COD containing in wastewater reduced to 64.3 mg/L from 1 622.9 mg/L, the figure before treatment. Three categories of PAM-containing wastewater in production practice have been treated with the COD removal ratios being 87.5%, 82.4% and 84.7% respectively. Presence of H_2O_2 and·OH are detected by means of Ti(Ⅳ)-5-Br-PADAP technique and colorimetry respectively. The concentration is positively proportional to the COD removal ratio and increases in accordance with increment of time of electrolysis and current.     

Study on the charge transference and local magnetic moment of yttrium-cobalt compound

The electronic charge transference and local magnetic moment of the YCo₅ intermetallic compound were calculated using SCF-MO-DVXα method and multiple cluster model. The result shows that about one 4d-electron is transferred from anY atom to Co₁(2c), and the calculated local spin magnetic moments of Co_I(2c) and Co_II(3g) atoms in YCo₅ compound are 1.33 and 1.48μ _B , respectively, which are in very good agreement with experiments. Supported by the National Natural Science Foundation of China Qiao Haoxue: born in Apr. 1970, Master     

超声波下酸化碘酸钾和亚硫酸钠反应的反应速率研究

分别测定在有超声波作用和在无超声波作用条件下 ,酸化碘酸钾 (KIO3 )和亚硫酸钠 (Na2 SO3 )反应的反应速率方程式及活化能 ,从而研究该反应的机理以及超声波在该反应中的作用 ,并确定反应的最佳条件。实验得出 ,超声波对该反应有一定的促进作用 ,但是这种促进作用只提高反应的速率常数和降低反应的活化能 ,并没有改变反应机理。在超声波功率为 30 0W时 ,反应的速率方程表示式为 :v =k·c1 0 9(KIO3 ) ·c1 0 0 (Na2 SO3 )·c1 0 8(H+ ) ,其中 :k =95 0 (mol-1·L) 2 ·s-1,活化能为 17 35kJ·mol-1。实验还得出 ,在温度为2 98K时 ,当KIO3 与Na2 SO3 的初始浓度比为 2∶5 ,H+ 的初始浓度为 0 0 4 2 8mol·L-1,超声功率为 30 0W时 ,反应速率为最快 ,即v =4 31× 10 -4mol·L-1·s-1)。