合成金属有机(高分子)铁磁体

本文介绍了纯有机(高分子)磁体及金属有机(高分子)磁体的种类、结构和发展慨况,并概述了近年来我们所合成的常温稳定二茂铁型有机(高分子)铁磁体及其应用前景.     

有机铁磁体的研究动态

着重介绍了有机铁磁体的研究动态，根据铁磁理论制造有机铁磁体的主要途径及有机金属复合物铁磁体与纯有机铁磁体，并对这２种有机铁磁体分子模型及其在目前所取得的研究成果做了较为详细的介绍与讨论。     

基于分子设计的有机铁磁体研究

有机铁磁体是材料科学中一个全新的研究领域,具有十分广阔的应用前景。由铁磁理论铁磁体可知物质的铁磁性来源于原子中未成对抵消电子的自旋（称之为顺磁中心）及自旋间的交换作用,因此可围绕如何引入顺磁中心及顺磁中心间的交换作用通过分子设计与化学合成而获得有机铁磁体。在本文中介绍了有机铁磁体分子设计的基本思想及目前最主要的几种有机铁磁体分子设计方法。并在文章的最后对作者近期在有机磁方面的研究工作进行了简要的总     

在外磁场中对铁磁体、反铁磁体、亚铁磁体的自旋波谱的讨论

在外磁场中我们用量子理论方法计算了铁磁体、反铁磁、亚铁磁体的自旋波谱,并对自旋波的特点进行了讨论。我们发现亚铁磁体既有类似于反铁磁体的磁序特性,又有类似于铁磁体的波谱特性。     

对铁磁体近似物态方程与相变的讨论

指出用铁磁体近似物态方程讨论铁磁体向顺磁体转变时的存在不合理性,并用热力学理论进行分析.     

有机铁磁体的研究进展及应用前景

阐述了有机铁磁体的研究动态。根据铁磁理论制造有机铁磁体的主要途径有有机金属复合物铁磁体与纯有机铁磁体,本文对这两种有机铁磁体特别是对纯有机铁磁体在目前所取得的研究成果做了较为详细的介绍与讨论,根据有机铁磁体的特性对有机铁磁体的应用前景进行了展望。     

有机高分子磁体的分子设计

对有机高分子磁体的分子设计研究进行了综述,讨论了设计有机高分子磁体主要的4种理论模型,即Heiter London自旋交换模型、分子间电子转移模型、高自旋多重度模型和超级交换模型,并对这一领域的发展和应用进行了展望.     

簡單鐵磁子理論的應用

1,引言应用自旋波方法以计算在低温范围内铁磁体,反铁磁体及亚铁磁体的磁化,许多作者得出较准确C.B.冯索夫斯基首先指出,在这种理论形式中,铁磁性应该彻底地作为一种多电子集体的合作现象来处理。在低温即     

准一维基于分子亚铁磁体自旋系统磁化率性质研究

基于交替自旋Ising—Hamiltonian模型,用量子转移矩阵方法,研究了不同外场条件下准一维基于有机分子亚铁磁体磁化率的结构序参量．对磁化率一的研究表明：双自由基和单自由基的交替有机自旋链的亚铁磁自旋排列等效于有效自旋S=1／2的铁磁相互作用链,双自由基有机高分子对具有单一成分的有机基于分子亚磁体具有绝对优势．量子Monte Carlo方法和精确对角化方法的计算结果两者相符,且与某些实验结果定性相符．     

与铁磁体耦合的分子结中电流生热性质研究

研究与两个铁磁导体耦合的分子结中电流的生热性质.发现当分子结的能级为零时,电流和热流在不同电压下随着两个铁磁体磁化强度的增加而单调变小.当两个铁磁体的磁化方向相互反平行时,电子的入射和透射隧穿速率随磁化强度的增大而变得相差更大,从而使得电流和热流被抑制的趋势更为明显.当电压取固定值时,电流和热流在不同的分子结能级条件下随着铁磁体磁化强度的增大而变小.同样地,当两个铁磁体的磁化方向为反平行时,电流和热流被抑制的趋势更为明显.     

Coexistence of ferromagnetism and metallic conductivity in a molecule-based layered compound

Crystal engineering--the planning and construction of crystalline supramolecular architectures from modular building blocks--permits the rational design of functional molecular materials that exhibit technologically useful behaviour such as conductivity and superconductivity, ferromagnetism and nonlinear optical properties. Because the presence of two cooperative properties in the same crystal lattice might result in new physical phenomena and novel applications, a particularly attractive goal is the design of molecular materials with two properties that are difficult or impossible to combine in a conventional inorganic solid with a continuous lattice. A promising strategy for creating this type of 'bi-functionality' targets hybrid organic/inorganic crystals comprising two functional sub-lattices exhibiting distinct properties. In this way, the organic pi-electron donor bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) and its derivatives, which form the basis of most known molecular conductors and superconductors, have been combined with molecular magnetic anions, yielding predominantly materials with conventional semiconducting or conducting properties, but also systems that are both superconducting and paramagnetic. But interesting bulk magnetic properties fail to develop, owing to the discrete nature of the inorganic anions. Another strategy for achieving cooperative magnetism involves insertion of functional bulky cations into a polymeric magnetic anion, such as the bimetallic oxalato complex [MnIICrIII(C2O4)3]-, but only insoluble powders have been obtained in most cases. Here we report the synthesis of single crystals formed by infinite sheets of this magnetic coordination polymer interleaved with layers of conducting BEDT-TTF cations, and show that this molecule-based compound displays ferromagnetism and metallic conductivity.     

C掺杂ZnO稀磁半导体的磁特性研究

利用基于密度泛函理论(DFT)的第一性原理计算方法,研究C掺杂ZnO稀磁半导体的磁性质.发现ZnO∶C体系的磁性来源于C-p和Zn-d轨道之间的杂化,铁磁性产生的机制是以巡游电子为媒介的铁磁交换作用.富O环境下制备ZnO∶C样品能够更好地在室温下得到稳定的铁磁有序.     

Electric-field control of ferromagnetism

It is often assumed that it is not possible to alter the properties of magnetic materials once they have been prepared and put into use. For example, although magnetic materials are used in information technology to store trillions of bits (in the form of magnetization directions established by applying external magnetic fields), the properties of the magnetic medium itself remain unchanged on magnetization reversal. The ability to externally control the properties of magnetic materials would be highly desirable from fundamental and technological viewpoints, particularly in view of recent developments in magnetoelectronics and spintronics. In semiconductors, the conductivity can be varied by applying an electric field, but the electrical manipulation of magnetism has proved elusive. Here we demonstrate electric-field control of ferromagnetism in a thin-film semiconducting alloy, using an insulating-gate field-effect transistor structure. By applying electric fields, we are able to vary isothermally and reversibly the transition temperature of hole-induced ferromagnetism.     

Superconductivity on the border of itinerant-electron ferromagnetism in UGe2

The absence of simple examples of superconductivity adjoining itinerant-electron ferromagnetism in the phase diagram has for many years cast doubt on the validity of conventional models of magnetically mediated superconductivity. On closer examination, however, very few systems have been studied in the extreme conditions of purity, proximity to the ferromagnetic state and very low temperatures required to test the theory definitively. Here we report the observation of superconductivity on the border of ferromagnetism in a pure system, UGe2, which is known to be qualitatively similar to the classic d-electron ferromagnets. The superconductivity that we observe below 1 K, in a limited pressure range on the border of ferromagnetism, seems to arise from the same electrons that produce band magnetism. In this case, superconductivity is most naturally understood in terms of magnetic as opposed to lattice interactions, and by a spin-triplet rather than the spin-singlet pairing normally associated with nearly antiferromagnetic metals.     

Zn1-xCrxO稀磁半导体薄膜的制备及磁性研究

采用磁控交替溅射方法和真空退火处理制备了Zn1-xCrxO薄膜,利用全自动X射线衍射仪和物理性质测量仪对样品的结构、晶粒尺寸及磁性等进行了测量和标度,得到了具有室温磁性的掺Cr的氧化锌基稀磁半导体.     

几种金属材料拉伸断裂断口磁性的电子显微研究

利用电子显微技术对几种金属材料拉伸断裂断口进行了分析,对它们的力学性能、拉伸磁性、断面微观结构进行了比较研究,得出了它们之间存在的一些特性,并从理论上作了一些初步的探讨。给出了铁磁体ΔＥ效应的应用。     

Origin of ferromagnetic exchange interactions in a fullerene-organic compound

Organic ferromagnets, which exhibit exchange interactions between unpaired electrons in pi-orbitals, are rare, and the origin of ferromagnetism in these compounds has so far remained unexplained. Tetrakis(dimethylamino)ethylene-fullerene[60] (TDAE-C60) shows a transition to a ferromagnetic state with fully saturated s = 1/2 molecular spins at the relatively high Curie temperature (for organic materials) of 16 K (ref. 4). It has been suggested that the orientations of the C60 molecules may be important for ferromagnetism in this material, but in the absence of structural data at low temperatures there has been little progress towards understanding these microscopic interactions. Here we report the results of a comparative structural study of two different magnetic forms of TDAE-C60 crystals at low temperatures, correlating the structural properties--in particular, the intermolecular orientations--with the magnetic properties. We find that both ferromagnetism and spin-glass-like ordering are possible in this material, and depend on the orientational state of C60 molecules. This resolves the apparent contradictions posed by different macroscopic measurements, and opens the way to a microscopic understanding of pi-electron ferromagnetic exchange interactions in organic materials.     

镍金属的光电子光谱研究

光电子光谱实验对许多材料物理性质 的理论解释给予了验证。对于镍金属的电导性与磁场性质给出了实验上的解释。通过试验，清楚的看出镍金属的3d－4s杂化及其非常高的3d态密度。由于杂化使得3d带的空穴参与了导电过程，而高的态密度使其具有的有效质量。这些发现都对镍金属弱导电性的理论解释做了支持。此外，从自旋一极化光电子光谱实验也显示了理论上对铁磁性本质解释－分子场（交换场）的存在。并讨论 实验与理论结果的差异。     

Al和氧空位对ZnO:Co稀磁半导体磁性质的影响

利用基于密度泛函理论的第一性原理计算方法,研究了Al共掺杂和氧空位缺陷对Co掺杂ZnO磁性质的影响,发现Al原子共掺杂引入的自由电子载流子会稳定体系的反铁磁性从而减弱Co原子间的铁磁性交换,而氧空位缺陷束缚的电子载流子对提高体系的铁磁性具有积极的作用.氧空位引入的电子载流子部分转移到Co原子和近邻Zn原子,形成以电子载流子为媒介的Co原子间的耦合作用,稳定体系的铁磁态,增强Co原子间的交换耦合作用.     

Low-temperature magnetic anomalies of oxygen-doped T′-type 214 compounds

A new low_temperature anomalous magnetism at about 29 K for the oxygen doped (Eu 1- x Y x ) 2CuO 4 and Sm 2CuO 4, prepared under high pressure, has been investigated. This anomaly originated from different mechanisms to weak ferromagnetism (WF) behavior of T′ phase, and should be assigned to the ferromagnetic clusters formed by doped holes.