Magnetic Correlation Engineering in Spin-Sandwiched Layered Magnetic Frameworks

The insertion of “sandwiched spins” between magnetic layers could efficiently affect the interlayer magnetic correlations, but doing so increases the complexity in the interlayer spin alignment because of competition between the inserted spin-layer interaction J_NNI and the interlayer through-space interaction J_NNNI if the magnitude of J_NNI is of the same order as J_NNNI with reciprocal signs of the respective interactions. Herein, systematic tuning of the magnetic phase variations by J_NNI and J_NNNI in two kinds of metal-variable isostructural series of supramolecular pillared layer magnets [MCp*₂][{Ru₂^II,II(2,3,5,6-F₄CO₂)₄}₂(TCNQ)] ⋅ 2 DCE (M=Co, Fe, Cr; 2,3,5,6-F₄PhCO₂⁻=2,3,5,6-tetrafluorobenzoate; TCNQ=7,7,8,8-tetracyano-p-quinodimethane; DCE=1,2-dichloroethane) and their DCE-free series, in which [MCp*₂]⁺ (Cp*=η⁵-C₅Me₅) species with S=0, 1/2, and 3/2 for M=Co, Fe, Cr, respectively, are sandwiched between ferrimagnetic layers of [{Ru₂}₂(TCNQ)]⁻, is demonstrated. The results showed that the flexible magnetic natures of these magnets are changeable in dependence on J_NNI and J_NNNI, as well as on interlayer inserted spins M.     

Magnetic organometallosiloxanes

The generalized analysis of a change in magnetic properties of organometallosiloxanes as a function of the number of metal atoms in their molecules (on going from mono- and binuclear to polynuclear crystalline and polymeric compounds) is presented. The relation between the magnetic characteristics and structural parameters of metal-containing fragments is studied. The factors affecting the formation of exchange-coupled ionic pairs and clusters in polymeric systems are analyzed. The ways to the organization of magnetic phases in polymeric systems are considered: the choice of conditions of chemical synthesis, the organization of metal atoms in a common spin system upon incorporation of conducting coordinating additives, and thermocondensation and reduction processes leading to the formation of a metallic phase dispersed in a silicon dioxide matrix. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1432–1442, August, 1997.     

磁性纳米包覆微球的制备和磁性表征

以胶体球形粒子为基体发展起来的纳米包覆(nano鄄coating)技术近来引起人们的极大兴趣,这种纳米包覆技术得到的产物常常被称为核壳粒子(core鄄shellparticles)。这种包覆一般是将纳米颗粒直接吸附在核微球上,或者包覆材料控制沉淀在核微球上[1,2]。这些复合微球常常展现出独特的光、电、力学、化学、催化等性质,因而具有广泛的研究和应用前景[3~7]。近十几年来,用做磁感应成像的超顺磁材料得到了深入的研究[4]。一方面,磁性颗粒的尺寸、电荷和表面成分对其应用有很大影响[8,9],另一方面,材料的磁学性质又主要取决于磁颗粒的大小[10]。Xu和Lindlar制备了含超顺磁颗粒的聚合物胶体颗粒,被用于构建超顺磁性的光子晶体[11,12]。在聚合物微粒上包覆氧化铁颗粒通常采用表面沉淀或表面改性官能团诱导反应包覆的方法。但这些方法不能很好控制复合微粒的均一性和表面平整性;Caruso的层鄄层包覆法(Layer鄄byLayer)虽然实现了磁性颗粒包覆[13],然而这种方法非常繁琐而不利于广泛应用。本文报道了一种新的合成磁性包覆颗粒的方法,即以聚合物微球为基核,通过非均相种子生长法包覆磁性纳米颗粒,并研究了...     

磁制冷

在当今世界,制冷起着非常重要的作用。如果没有制冷技术,我们要想获得新鲜的食物,依然要受季节以及地域的限制。调节环境温度使生活环境变得舒适也将成为不可能的事情。而且,一些医疗方面的前沿技术,如核磁共振成像,器官移植,器官和组织的低温储藏,以及低温外科手术等都将不复存在。制冷技术自100多年前被发明以来基本上没有本质上的改变。现代制冷技术基本上都是基于气体压缩/膨胀的制冷循环过程,这一过程是一个高能耗过程,每年大约会消耗109kW的电能。现有制冷技术的制冷效率已经接近了它的理论极限,而这个极限远远小于根据卡诺循环计算得到的最大理论效率。此外,那些被用作制冷工质,且最终会进入环境中的液态化学物质,不仅可以破坏臭氧层,使得全球气候变暖,还有一些本身就是有害的气体(如NH3气)。1997年的两个巨大突破向人们展现了一种新的制冷方式———磁制冷,这种制冷技术是一种绿色环保制冷技术,效率高,而且能进行循环交替制冷。第一个突破是1997年2月往复式结构磁制冷样机的成功研制[1]。这台机器利用超导磁体产生磁场(最大5 T)。在5 T的磁场强度下,最大制冷量可达600 W,COP值最大可达15,效率接近卡诺循环的60%,温跨...     

Magnetic titrations

Magnetic titrations using a new titration cell and procedure are described. The paramagnetism of a hexammine nickel nitrate solution decreases linearly upon the addition of cyanide up to the endpoint (complete formation of Ni(CN)₄^2-) ; there is no evidence of the formation of intermediate complexes. Intermediate complexes are evident in the titrations of iron(II) with 1,10-phenanthroline and with 2,2'-bipyridyl; log K₁ values, calculated from the magnetic data, are 6.0 and 5.0 respectively.     

LaFe13-xSix (1.2≤x≤2.2)化合物的磁场诱导熵变与磁场的关系

通过真空电弧熔炼、长时间真空热处理的方法获得了单相NaZn13-型LaFe13-xSix(1.2≤x≤2.2)化合物,并测量了它们的磁化强度与磁场和温度的关系,用Maxwell关系式计算出在不同磁场下化合物的熵变ΔS。用Landau的二级相变理论及平均场近似下的标度律,分析拟合了LaFe13-xSix化合物ΔS与H之间的关系,对于具有一级和二级相变的材料,发现均存在ΔS∝H2/3的关系,只是拟合得到的参数不同。采用熵变峰值拟合得到的参数能够反映材料中一级磁性相变的程度,研究磁场诱导的熵变与磁场的关系可以为磁制冷研制提供指导。     

Magnetic Fluid Structural Transformations in Electric and Magnetic Fields

Periodic structural lattices formed in thin layers of an originally uniform magnetic fluid exposed to a constant electric field were studied experimentally. Peculiarities of their transformations under the effect of an additional magnetic field were described. The structural transformations and the development of an electrohydrodynamic instability in an aggregated magnetic fluid subjected to both alternating electric and constant magnetic fields were investigated. The observed patterns of the light diffraction on the studied structures were reported.     

纳米晶稀土永磁材料的制备和磁性

介绍了纳米晶稀土永磁材料的制备和磁性方面的有关研究工作, 主要内容有: 低钕快淬Fe3B基钕铁硼新型纳米晶复合稀土永磁材料的相结构与磁性, 快淬Pr2Fe14B/α-Fe型纳米复合稀土永磁材料的微结构与永磁性, 快淬Sm-Co基稀土永磁材料的织构与磁各向异性的关系, 以及纳米晶稀土永磁材料的矫顽力机制和模拟计算研究等.     

磁流体制备中磁性颗粒的表面处理

磁流体制备中磁性颗粒的表面处理;磁流体; 紫外光谱分析法; 油酸; 表面处理     

D-和L-丙氨酸的低温磁相变——磁场变化下的比热和直流磁化率(英文)

为了解D-和L-丙氨酸单晶晶格在极低温下是否存在磁手性相变,在2-20 K下改变磁场强度(0,1,3,5T)测定其比热.实验结果表明比热和温度之间的函数关系很好地符合C(T)=aT3+b/T2方程,其中aT3项为晶格声子的贡献,可由公式CV=(12/5)π4R(T/ΘD)3来描述(ΘD为德拜温度),b/T2项为磁场对比热的贡献.实验发现,在2-20 K范围内D-和L-丙氨酸单晶在不同磁场强度下均存在Boson峰(在Cp/T3-T曲线中表现为一个最大值).磁的贡献导致D-和L-丙氨酸单晶的四条Cp/T3-T曲线在2-12 K时不重合,且在12-20 K时消失,此即Schottky反常.零磁场下,D-和L-丙氨酸的Boson峰分别为9.44和10.86 K;德拜温度分别为151.5和152.7 K.结合磁场强度1 T下的直流磁化率测定,发现在温度低于5 K时,D-和L-丙氨酸单晶有相反的磁化率行为,反映了核自旋和电子自旋弱相互作用的手性表现.     

Self-Assembly Anisotropic Magnetic Nanowire Films Induced by External Magnetic Field

Self-assembly generated materials induced by an external magnetic field have attracted considerable interest following the development of nanodevices. However, the fabrication of macroscopic and anisotropic magnetic films at the nanoscale remains a challenge. Here, anisotropic magnetic films are successfully prepared using a solution-based nanowire assembly strategy under a magnetic field. The assembly process is manipulated by changing the thickness of silica shell coated on the surface of magnetic nanowires. The anisotropic magnetic films show highly anisotropic magnetization under different angles of magnetic field and better magnetization properties than that of disordered magnetic films. The well-defined nanowire arrays enable magnetization anisotropic property which may be useful in the magnetic energy conversion technologies and biomedical sciences which lie far beyond those achievable with traditional magnetic materials.     

Electrical Properties of Chain Microstructure Magnetic Emulsions in Magnetic Field

The work deals with the experimental study of the emulsion whose dispersion medium is a magnetic fluid while the disperse phase is formed by a glycerin-water mixture. It is demonstrated that under effect of a magnetic field chain aggregates form from the disperse phase drops. Such emulsion microstructure change affects its macroscopic properties. The emulsion dielectric permeability and specific electrical conductivity have been measured. It is demonstrated that under the effect of relatively weak external magnetic fields (～1 kA/m) the emulsion electrical parameters may change several fold. The work theoretically analyzes the discovered regularities of the emulsion electrical properties.     

磁性高分子微球

对磁性高分子微球的研究现状进行了综述,详细探讨了目前常用的各种合成制备方法,并对各种方法的优缺点进行了分析。在此基础上,对磁性高分子微球在细胞分离、有机合成、环境/食品微生物检测等领域的最新应用进展及存在的问题进行了分析,指出了该领域今后的研究方向。     

Magnetic Helical Micromachines

Helical microrobots have the potential to be used in a variety of application areas, such as in medical procedures, cell biology, or lab‐on‐a‐chip. They are powered and steered wirelessly using low‐strength rotating magnetic fields. The helical shape of the device allows propulsion through numerous types of materials and fluids, from tissue to different types of bodily fluids. Helical propulsion is suitable for pipe flow conditions or for 3D swimming in open fluidic environments.     

深冷状态下纳米镝铁氧体磁粒子磁性能的研究

采用湿化学法制备出稀土Dy3+掺杂的纳米Fe3O4磁粒子,用月桂酸进行了表面修饰,研究了磁粒子在室温和深冷(200.2～56.5 K)状态下的磁性能.经X射线衍射分析发现,适量的Dy3+掺杂不会改变纳米Fe3O4磁粒子的晶型结构.透射电镜(TEM)照片表明,制备出的纳米磁粒子成球性好,且大部分磁粒子的粒径在14 nm左右.通过磁性测量仪、振动样品磁强计(VSM)对磁性能进行了表征.磁化曲线表明掺杂引起磁性能发生变化,磁粒子室温下无剩磁和矫顽力,具有超顺磁性;深冷状态下出现剩磁和矫顽力,且随温度的降低,剩磁和矫顽力增大,不具有超顺磁性,饱和磁化强度略高于室温值.     

Magnetic particle nanorheology

We investigate the employment of AC susceptometry as a novel method to extract frequency- and scale-dependent rheological properties of soft materials. The approach makes use of the interrelation between the magnetic susceptibility of magnetically blocked tracer particles and the mechanical modulus of the matrix as experienced on the particle scale. We report susceptibility measurements on aqueous solutions of ethylene glycol, triethylene glycol, or poly-(ethylene glycol), using CoFe₂O₄ nanoparticles as tracer particles, in the frequency range of 1 Hz–250 kHz. Frequency-dependent rheological properties, including viscosity and loss moduli, of the solutions were obtained by applying an extended Debye relaxation model and a method analogous to the Gemant-DiMarzio-Bishop approach.     

Magnetic isotope effect

The electron spin selectivity of radical reactions is accompanied by nuclear spin selectivity, i.e., sorting of the isotopic nuclei relative to their magnetic moment. This property of spin-selective reactions produces separation of magnetic and nonmagnetic isotopes known as the magnetic isotope effect. The chemical physics of this phenomenon is examined along with the conditions and magnitude of its manifestation as well as the prospects for its use in theoretical and experimental chemistry.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 31, No. 3, pp. 144–152, May–June, 1995.     

一种新型的纳米功能材料:磁性纳米镁铝水滑石

本文将磁性基质与镁铝水滑石进行组装首次合成出一种新型的纳米磁性功能材料—磁性纳米镁铝水滑石。这种新型纳米功能材料的XRD及TA结果表明,镁铝水滑石赋予磁性后并没有改变其层状结构的典型特征。样品的TEM图表明,磁性基质的加入后样品的颗粒粒径并没有明显增大,且保持在20～50nm之间。对磁性镁铝水滑石磁性能的考察结果表明,样品的比饱和磁化强度随磁性基质含量的增加而线性增加。     

电沉积铁族薄膜的磁性圆二色研究

采用循环伏安法在GaAs(100)单晶表面电沉积了铁族金属单质薄膜. 扫描电子显微镜(SEM)结果显示, Fe族金属薄膜的晶粒较小, 薄膜平整度较高。通过X射线衍射(XRD)谱分析了Fe, Co, Ni在GaAs(100)晶面上的外延生长. 使用磁光克尔效应装置研究了Fe族金属薄膜的宏观磁性, 用同步辐射圆偏振软X射线测量了铁族单质磁性薄膜的吸收谱, 获得了X射线磁性圆二色谱, 并通过加和定则计算了磁性薄膜中Fe族金属原子的轨道磁距和自旋磁矩.