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.     

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...     

单分子磁体研究的最新进展

宏观上表现出可测的慢磁弛豫行为的单个分子称为单分子磁体,它主要包括过渡金属单分子磁体和稀土单分子磁体,其在量子计算、高密度信息存储以及自旋器件等方面的潜在应用吸引了研究者的广泛关注.本文介绍了单分子磁体研究的最新进展,重点总结了构筑高性能单分子磁体的合成策略.     

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.     

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.     

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.     

3d过渡金属单离子磁体

单分子磁体在量子计算、高密度存储材料以及分子自旋电子学等领域具有广阔的应用前景。3d过渡金属单离子磁体具有结构简单、易于研究磁构关系以及可控配体场获得高能垒等特点,因而成为近年来单分子磁体领域的研究热点。本文结合现有研究成果,从配位构型出发,旨在对近年来基于3d过渡金属离子的单离子磁体进行综述,重点阐述配体场、磁各向异性和单离子磁体性质三者之间的关系,为设计合成单分子磁体提供新的思路。     

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.     

单离子磁体及其磁弛豫动力学的研究进展

单分子磁体因其在高密度信息存储、自旋电子学以及量子计算方面有潜在的应用价值而被广泛关注。单离子磁体是具有单个金属自旋中心的单分子磁体,其特点是结构简单、可设计性强和磁构关系更易研究。本文介绍了近年来典型的单离子磁体及其磁弛豫动力学的研究进展。     

基于顺磁稀土离子的磁性分子材料

构建含镧系稀土金属离子的分子基磁性材料是当前分子磁学研究的重要领域之一．本文按照单稀土离子,稀土离子-稀土离子（4f-4f）相互作用体系,稀土离子．过渡金属离子（4f-3d）相互作用体系,稀土离子．自由基（4f-p）相互作用体系的顺序,介绍了含镧系稀土金属离子的单离子磁体,基于稀土金属离子,过渡金属离子和自由基多核簇的单分子磁体、单链磁体和磁有序体系的磁学性质．根据磁性分子材料中自旋载体和磁耦合性质的不同,分别用实例介绍了磁耦合、磁有序和磁驰豫性质的特点和来源．首先,本文综述了孤立的单稀土离子配合物体系的结构和磁学性质．由于稀土金属离子的4f电子具有强的旋轨耦合作用和较大的磁各向异性,所以有些单稀土离子配合物如双酞菁铽、镝等体系具有慢的磁驰豫行为,其低温下的磁滞回线呈现台阶状,被称为单离子磁体．该类分子基磁性配合物慢磁驰豫性质的来源可以用镧系稀土离子的电子自旋磁矩、轨道磁矩、核自旋磁矩之间的相互作用解释．具有场诱导缓慢磁驰豫行为的单稀土离子配合物是另一类引起关注的磁性分子材料．该类配合物在零场下交流磁化率的虚部没有峰值,而在一定的外磁场下,其交流磁化率的虚部出现峰值并具有频率依赖性．这种现象可能可以归因为体系的Kramer简并基态在外场下消除了快的磁驰豫过程,使慢的磁驰豫过程,如Orbach过程成为主导．其次,本文综述了稀土离子的4f电子之间的磁耦合作用和磁学性质．一方面,对于具有4f^7电子构型的含Gd（III）离子配合物,f电子之间的磁耦合作用主要是各向同性磁交换作用．由于4f电子能量很低,同其他稀土离子f电子之间的耦合作用被外层轨道屏蔽,所以磁耦合常数很小,无法形成磁有序的结构;另一方面,对于有强旋轨耦合作用的非4f^7电子构型的稀土离子配合物,由于理论计算和拟合上的困难,其4f电子之间的磁耦合作用的机理研究还很少．值得关注的是,有报道发现Dy3簇合物具有单分子磁体的性质,并且基态几乎是非磁的,其磁性来源主要是丰富的低激发态能谱,也就是说,一般认为的单分子磁体必须具有大的自旋基态并不是发生缓慢磁驰豫行为的必要条件．再次,本文综述了稀土金属离子一过渡金属离子簇合物的磁学性质．由于4f-3d之间的磁耦合作用要远大于4f-4f电子之间的磁耦合作用,所以此类配合物磁学性质和磁构关系的研究相对较多,其磁学性质也相对丰富．由于Gd离子和Cu离子的旋轨耦合作用较小,理论计算和磁性数据的拟合相对简单,所以对于磁构关系和磁耦合性质的研究主要集中在Gd—Cu体系．对于存在强旋轨耦合作用的其他镧系稀土离子,可能出现磁有序,慢的磁驰豫等其他磁学现象．实验上也合成了一些基于4f-3d作用的单分子磁体和单链磁体．此外,本文还综述了稀土金属离子．自由基体系的磁学性质．对于自由基与稀土金属离子之间的耦合,由于不需要通过抗磁性的其他原子,所以可能产生比4f-4f,4f-3d体系更强的磁耦合作用．实验上,也的确发现了一些具有磁有序行为的4f-自由基分子磁性材料,但磁有序主要发生在低温区．最后,对稀土分子基磁性材料研究中需要解决的问题和未来发展前景进行了展望．     

Heterometallic 3d–4f Complexes as Single‐Molecule Magnets

Heterometallic 3d‐4f complexes are being investigated, for some time, as being useful in molecular magnetism, particularly as single‐molecule magnets (SMMs). This interest is primarily because of the possibility of an increased ligand‐mediated super‐exchange phenomenon between the 3d and 4f metal ions. Such an interaction, apart from bestowing a favorable ground‐state spin to the complex, also assists in reducing quantum tunneling of magnetization that is widely prevalent in SMMs making them to lose magnetization. However, assembling both 3d as well as 4f ions using same ligand system is challenging and involves the design of multi‐site coordination ligands with specific coordination compartments for the 3d and the 4f metal ions while at the same time allowing these disparate metal ions to be linked to each other through a bridging ligating atom. This review presents a summary of the 3d‐4f complexes primarily derived from the author's work while alluding to important examples from the literature. We also provide an outlook for the future design of such complexes.     

Nuclear spin driven quantum tunneling of magnetization in a new lanthanide single-molecule magnet: bis(phthalocyaninato)holmium anion

The first measurements of magnetization hysteresis loops on a diluted single crystal of [(Pc)2Ho]-.TBA+ (Pc = phthalocyaninato, TBA = tetrabutylammonium) in the subkelvin temperature range are reported. Characteristic staircase-like structure was observed, indicating the occurrence of the quantum tunneling of magnetization (QTM), which is a characteristic feature of SMMs. The quantum process in the new lanthanide SMMs is due to resonant quantum tunneling between entangled states of the electronic and nuclear spin systems, which is an essentially different mechanism from those of the known transition-metal-cluster SMMs. Evidence of the two-body quantum process was also observed for the first time in lanthanide complex systems.     

Review: Single-molecule magnets based on pyridine alcohol ligands

Single-molecule magnets (SMMs) have attracted attention due to their potential applications in quantum computation and information storage, and many SMMs have been reported in the past two decades. In this review, we summarize the structures and the magnetic exchange interactions of pyridine alcohol-based SMMs to give a possible relationship between structure and magnetic property, providing information to generate new molecule-based magnetic materials. According to the correlated metal centers, these SMMs are separated into three segments to discuss.     

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.     

High-spin molecules with magnetic anisotropy toward single-molecule magnets

High-spin molecules with easy-axis magnetic anisotropy show slow magnetic relaxation of spin-flipping along the axis of magnetic anisotropy and are called single-molecule magnets (SMMs). SMMs behave as molecular-size permanent magnets at low temperature and magnetic relaxation occurs by quantum tunneling processes; such molecules are promising candidates for use in quantum devices. We first discuss intramolecular ferromagnetic interactions for preparing high-spin molecules. Second, we determine the magnetic anisotropy for single metal ions with d(n) configurations and discuss how molecular anisotropy arises from single-ion anisotropy of the assembled component metal ions.     

Development of Single‐Molecule Magnets†

Single‐molecule magnets (SMMs) are paramagnetic molecules that can be magnetized below a certain temperature and have potential applications in high‐density information storage, magnetic qubits, spintronic devices, etc. The discovery of the first SMM, Mn₁₂, opened a new era of molecular magnetism and promoted collaborative researches between chemists and physicists for their exotic quantum as well as classical magnetic properties. In the recent past, great efforts have been made to develop strategies for constructing new SMMs with high energy barriers (U_eff) and blocking temperatures (T_B), resulting in great and fast development of SMMs. In this concise review, we highlight the main synthetic approaches and representative results in the design and synthesis of high performance SMMs. We hope to give the readers a basic understanding of SMMs and a snapshot of the representative researches on SMMs from a perspective of synthetic chemists.     

Oximate-bridged trinuclear Dy-Cu-Dy complex behaving as a single-molecule magnet and its mechanistic investigation

Lanthanide ions are supposed to be promising candidates for the elements of single-molecule magnets (SMMs) because of the large magnetic momentum and anisotropy. We have established the [Dy2Cu] complex as a new SMM. A plausible mechanism for quantum tunneling of magnetization is proposed for the first time among the 4f-3d heterometallic SMMs. The magnetic coupling parameter between Dy and Cu ions was well-defined as -0.155 K.     

Magnetic anisotropies in paramagnetic polynuclear metal complexes

The study of the magnetic properties of highly anisotropic paramagnetic molecules is an area of intense current research interest. Of these, single-molecule magnets (SMMs) and single-chain magnets (SCMs) showing non-equilibrium magnetization have remained a key topic over the past two decades. The slow magnetization reversals found in SMMs and SCMs are contingent on two requirements: a large ground-state spin forbidding direct quantum transitions of spin reversal, and a series of excited spin levels, due to the anisotropy of the system, which can act as steppingstones for the thermal relaxation of the spin orientations (the Orbach process). In this critical review, the latter requirement, i.e. the existence of magnetic anisotropies in paramagnetic species, is reviewed with the aim of providing clues towards the rational design of molecule-based magnets (100 references).     

Molecular Spintronics Based on Single‐Molecule Magnets Composed of Multiple‐Decker Phthalocyaninato Terbium(III) Complex

Unlike electronics, which is based on the freedom of the charge of an electron whose memory is volatile, spintronics is based on the freedom of the charge, spin, and orbital of an electron whose memory is non‐volatile. Although in most GMR, TMR, and CMR systems, bulk or classical magnets that are composed of transition metals are used, this Focus Review considers the growing use of single‐molecule magnets (SMMs) that are composed of multinuclear metal complexes and nanosized magnets, which exhibit slow magnetic‐relaxation processes and quantum tunneling. Molecular spintronics, which combines spintronics and molecular electronics, is an emerging field of research. Using molecules is advantageous because their electronic and magnetic properties can be manipulated under specific conditions. Herein, recent developments in [LnPc]‐based multiple‐decker SMMs on surfaces for molecular spintronic devices are presented. First, we discuss the strategies for preparing single‐molecular‐memory devices by using SMMs. Next, we focus on the switching of the Kondo signal of [LnPc]‐based multiple‐decker SMMs that are adsorbed onto surfaces, their characterization by using STM and STS, and the relationship between the molecular structure, the electronic structure, and the Kondo resonance of [TbPc₂]. Finally, the field‐effect‐transistor (FET) properties of surface‐adsorbed [LnPc₂] and [Ln₂Pc₃] cast films are reported, which is the first step towards controlling SMMs through their spins for applications in single‐molecular memory and spintronics devices.     

Controlled association of single-molecule magnets (SMMs) into coordination networks: towards a new generation of magnetic materials

The field of molecular magnetism has rapidly expanded since the discovery of single-molecule magnets (SMMs) at the beginning of the 1990s. Numerous SMMs have been studied and a broad community currently works on these systems to improve their magnetic characteristics. However, it has also become an important strategy to diversify a part of our research activity toward the organization of these magnetic molecules in order to move closer to future applications. One of the possible ways is to utilize SMMs as molecular building blocks and assemble them with the help of coordination chemistry. This strategy presents a significant challenge since the intrinsic magnetic properties of the parent SMMs can be modified, which consequently also provides a unique opportunity to investigate new behaviours at the frontier between SMMs and classical bulk magnets. Furthermore, the design of systems with "enhanced" SMM properties or magnet behaviour is theoretically possible by choosing coordinating linkers that could favour an effective ferromagnetic arrangement of the SMMs. In this perspective article, we will give an overview of the known networks based on SMMs with an emphasis on the synthetic strategies, magnetic properties, and finally possible routes to a new generation of molecular magnetic materials.