稀土单分子磁体的研究进展

在信息存储和量子计算方面具有广阔应用前景的单分子磁体及相关研究中,应用各向异性显著的稀土离子以期提高单分子磁体自旋翻转能垒的研究倍受关注。 本文综述了稀土单分子磁体的研究进展,并着重介绍了单核、三核及四核镝配合物单分子磁体的磁学性质。     

环形镧系分子簇合物的组装与单分子磁体性质

由于稀土离子具有很强的磁各向异性,近年来基于单核或多核稀土化合物的单分子磁体研究得到了人们广泛的关注.环形簇合物是一类特殊的簇合物,也称分子轮或金属冠醚.设计合成环形稀土簇合物不仅可以获得新的稀土单分子磁体,而且环形簇合物中稀土离子磁偶极的涡旋分布还可以产生环形磁矩,因而在量子计算、信息存储、自旋分子器件等方面具有潜在的应用.鉴于环形稀土簇合物特别是含奇数核的环形簇合物的合成依然充满挑战,本综述将着重阐述已报道的环形稀土簇合物的组装规律、结构特点及磁性研究.     

3d-4f单分子磁体

单分子磁体是指那些在磁场下能够被磁化,当磁场去除后仍能保持磁性的单个分子。由于在信息处理和储存方面具有潜在的广泛应用前景,单分子磁体日益成为化学、材料科学和物理等学科的研究热点。近年来,同时含有镧系金属离子和过渡金属离子的3d-4f单分子磁体更是引起了很多研究者的兴趣。本文阐述了3d-4f单分子磁体的优势,总结了3d-4f单分子磁体的常见合成方法及其磁性,分析了影响3d-4f单分子磁体磁性的因素。     

单分子磁体及其磁学表征*

单分子磁体是介于分子基磁体和纳米磁性材料的学科交叉点.对其不同寻常磁特性的研究不仅有助于纳米磁性离子物理学和化学的发展,而且有望最终用于高密度信息储存设备.本文就单分子磁体的研究背景和意义、单分子磁体的种类、结构及磁学表征作一概述.     

基于[Dy4（μ4-O）]四面体结构单元的八核和十核镝簇合物的合成、结构及其单分子磁体行为研究

通过溶剂热法合成了两个稀土簇合物,其组成分别为:[Dy8(bpt)8(μ4-O)2(μ-OMe)8(μ1,1,3,3-N3)(μ1,3-N3)(N3)2]11H2O 9MeOH(1)和[Dy10(bpt)6(μ4-O)4(μ3-OMe)4(μ-OMe)8(μ-OAc)2(OAc)2]40H2O(2)(Hbpt=3,5-双(2-吡啶基)-1,2,4-三氮唑).1的簇核结构由两个[Dy4(μ4-O)]四面体通过罕见的μ1,1,3,3和μ1,3叠氮桥连接而成,2则由四个共边连接的[Dy4(μ4-O)]四面体组成.两个簇合物都表现出单分子磁体行为,其中2是核数最高的纯稀土单分子磁体.     

稀土单分子磁体

单分子磁体因其磁性双稳态和慢弛豫机制而在超高密度存储材料、自旋电子器件等领域具有潜在的应用. 稀土单分子磁体因为具有较大的磁矩和磁各向异性而成为近年来研究的热点话题. 目前有关稀土单分子磁体的综述都主要集中在它们的合成、结构及磁性能, 而在其它性质方面缺少深入而系统的研究. 因此, 本论文结合现有的研究成果, 围绕稀土单分子磁体的高翻转能垒、复杂的多弛豫机制、可调控的磁性以及多功能材料的四个特点进行了综述, 旨在更好的理解稀土单分子磁体的物理、化学本质, 为稀土单分子磁体的设计与调控提供思路.     

锕系单分子磁体研究进展

单分子磁体是一类由单个分子组成的磁性材料,其磁性起源于单个分子的磁矩,有望在超高密度存储、量子计算机、自旋电子学等领域得到应用.由于锕系元素极大的旋轨耦合效应及5f轨道的延展性,锕系单分子磁体越来越受到人们的关注,期待未来磁学性能甚至能超越过渡及镧系金属.然而,目前对于锕系单分子磁体的弛豫机理及慢磁行为的影响因素仍尚未明确.本综述总结了近10多年以来报道的锕系单分子磁体,发现有效能垒的实验值和理论值极不相符,一定程度限制了锕系单分子磁体的发展.最后,对未来的锕系单分子磁体研究方向进行了展望.     

稀土单分子磁体研究进展

单分子磁体是一类纳米尺度的磁性材料,在高密度信息存储、量子比特和自旋电子器件等方面具有潜在的应用价值而备受关注.由于稀土离子具有大的磁矩和强的磁各向异性,稀土离子在高性能单分子磁体构筑方面有过渡金属离子不可比拟的优势.近年来,以单核和双核稀土单分子磁体为代表的稀土单分子磁体的研究取得了长足的进展,尤其是突破了以液氮沸点...     

单分子磁环最新进展及研究展望

与单分子磁体的定义(SMMs)相类似,单分子磁环(SMTs)定义为具有环形磁双稳态的一类分子。该类配合物的特征在于弱耦合磁矩的"涡旋"空间分布导致总磁矩为零,但是分子仍具有环形磁矩。单分子磁环为量子计算和信息存储提供了广阔的应用前景,也可以作为具有磁电耦合效应的多铁材料。自从在[Dy3]分子中首次观察到典型的单分子磁环行为以来,研究人员在合成单分子磁环方面做出了巨大的努力,致力于合成具有环形磁矩的分子以及设法将环形磁矩增强。本文将对近年报道的新兴单分子磁环配合物进行详细地分析讨论,旨在阐明影响环形磁矩排列的因素以及单分子磁环配合物的综合设计策略,指导探索合成具有增强环形磁矩的单分子磁环配合物。     

多酸构筑的单分子磁体

设计合成具有单分子磁体行为的分子磁性材料近年来受到广泛关注. 合成单分子磁体的一个常用策略是利用有机多齿含氧或含氮配体将各种自旋载体组装成簇,使之具有高基态自旋值(S)和负的单轴磁各向异性值(D),进而满足形成单分子磁体所需的磁能垒. 令人感兴趣的是近年来多酸发展成为一类构筑新型单分子磁体的无机建筑基元. 多酸是一类独特的具有富氧表面、可控的尺寸、形状和电荷的无机纳米级金属氧簇,同时,一系列缺位多酸衍生物能够结合各种过渡金属或稀土离子形成多核金属簇合物. 近五年来,多酸已作为一类无机多齿含氧配体成功构筑系列具有单分子磁体行为的新型过渡金属簇合物、稀土簇合物和3d-4f杂金属簇合物. 特别是一些缺位多酸配体能够为稀土离子提供完美的配体场,进而构筑新一代的单离子磁体. 此外,高自旋、磁各向异性单元(如单分子磁体)还可被均匀分散在具有孔道特征的多酸三级结构中,形成具有单分子磁体行为的多酸基复合材料. 最近,以多酸为模板构筑具有单分子磁体行为的多核簇合物也取得了新进展. 本综述旨在对近五年来利用多酸构筑的单分子磁体化合物进行评论,重点阐述利用多酸设计合成单分子磁体的策略、多酸在单分子磁体化合物结构中的作用和优势,以及多酸构筑单分子磁体这一研究课题的发展前景.     

单链磁体及其研究进展

单链磁体是继单分子磁体之后分子磁学领域的又一前沿课题。对其磁特性的研究不论是在基础理论方面还是在实际应用方面都具有非常重大的意义。本文较全面地介绍了现有单链磁体的种类、结构、磁学研究方法,并对其研究方向进行了展望。     

Recent Developments in Lanthanide Single‐Molecule Magnets

Single‐molecule magnets (SMMs) exhibiting slow relaxation of magnetization of purely molecular origin are highly attractive owing to their potential applications in spintronic devices, high‐density information storage, and quantum computing. In particular, lanthanide SMMs have been playing a major role in the advancement of this field because of the large intrinsic magnetic anisotropy of lanthanide metal ions. Herein, some recent breakthroughs that are changing the perspective of the field are highlighted, with special emphasis on synthetic strategies towards the design of high‐performance SMMs.     

Quantum Spin Dynamics in Molecular Magnets

Summary.  The detailed theoretical understanding of quantum spin dynamics in various molecular magnets is an important step on the roadway to technological applications of these systems. Quantum effects in both ferromagnetic and antiferromagnetic molecular clusters are, by now, theoretically well understood. Ferromagnetic molecular clusters allow one to study the interplay of incoherent quantum tunneling and thermally activated transitions between states with different spin orientation. The Berry phase oscillations found in Fe₈ are signatures of the quantum mechanical interference of different tunneling paths. Antiferromagnetic molecular clusters are promising candidates for the observation of coherent quantum tunneling on the mesoscopic scale. Although challenging, application of molecular magnetic clusters for data storage and quantum data processing are within experimental reach already with present day technology. Corresponding author. E-mail: Daniel.Loss@unibas.ch Received May 7, 2002; accepted May 22, 2002     

Quantum tunneling of magnetization and related phenomena in molecular materials

Molecules comprising a large number of coupled paramagnetic centers are attracting much interest because they may show properties which are intermediate between those of simple paramagnets and classical bulk magnets and provide unambiguous evidence of quantum size effects in magnets. To date, two cluster families, usually referred to as Mn12 and Fe8, have been used to test theories. However, it is reasonable to predict that other classes of molecules will be discovered which have similar or superior properties. To do this it is necessary that synthetic chemists have a good understanding of the correlation between the structure and properties of the molecules, for this it is necessary that concepts such as quantum tunneling, quantum coherence, quantum oscillations are understood. The goal of this article is to review the fundamental concepts needed to understand quantum size effects in molecular magnets and to critically report what has been done in the field to date.     

The Role of Radical Bridges in Polynuclear Single-Molecule Magnets

Employing radical bridges between anisotropic metal ions has been a viable route to achieve high-performance single-molecule magnets (SMMs). While the bridges have been mainly considered for their ability to promote exchange interactions, the crystal-field effect arising from them has not been taken into account explicitly. This lack of consideration may distort the understanding and limit the development of the entire family. To shed light on this aspect, herein we report a theoretical investigation of a series of N -radical-bridged diterbium complexes. It is found that while promoting strong exchange coupling between the terbium ions, the N -radical induces a crystal field that interferes destructively with that of the outer ligands, and thus reduces the overall SMM behavior. Based on the theoretical results, we conclude that the SMM behavior in this series could be further maximized if the crystal field of the outer ligands is designed to be collinear with that of the radical bridge. This conclusion can be generalized to all exchange-coupled SMMs.     

Butterfly‐Shaped Pentanuclear Dysprosium Single‐Molecule Magnets

Two new “butterfly‐shaped” pentanuclear dysprosium(III) clusters, [Dy₅(μ₃‐OH)₃(opch)₆(H₂O)₃] ? 3 MeOH ? 9 H₂O ( 1 ) and [Dy₅(μ₃‐OH)₃(Hopch)₂(opch)₄(MeOH)(H₂O)₂] ? (ClO₄)₂ ? 6 MeOH ? 4 H₂O ( 2 ), which were based on the heterodonor‐chelating ligand o‐vanillin pyrazine acylhydrazone (H₂opch), have been successfully synthesized by applying different reaction conditions. Single‐crystal X‐ray diffraction analysis revealed that the butterfly‐shaped cores in both compounds were comparable. However, their magnetic properties were drastically different. Indeed, compound 1 showed dual slow‐relaxation processes with a transition between them that corresponded to energy gaps (Δ) of 8.1 and 37.9 K and pre‐exponential factors (τ₀) of 1.7×10^?5 and 9.7×10^?8 s for the low‐ and high‐temperature domains, respectively, whilst only a single relaxation process was noted for compound 2 (Δ=197 K, τ₀=3.2×10^?9 s). These significant disparities are most likely due to the versatile coordination of the H₂opch ligands with particular keto–enol tautomerism, which alters the strength of the local crystal field and, hence, the nature or direction of the easy axes of anisotropic dysprosium ions.