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.     

单分子磁体

单分子磁体是涉及合成化学、材料科学和凝聚态物理等边缘学科的一个新颖课题。本文对单分子磁体的主要性质、功能、研究方法和最新进展做了评述。重点介绍了含Mn和Fe这两类重要的单分子磁体。     

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...     

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。     

单分子磁体[Mn4(CF3COO)4(hmp)6]的合成、晶体结构及磁学性质

以[Mn12O12(CF3COO)16(H2O)4]·2CF3COOH·4H2O和2-羟甲基吡啶(hmpH)为起始物, 在四氢呋喃溶液中合成了一种新的四核锰配合物[Mn4(CF3COO)4(hmp)6]. X射线单晶衍射结果表明, 该配合物属于单斜晶系, P21/c空间群, 晶胞参数a=1.3663(3) nm, b=1.4705(3) nm, c=1.4734(3) nm, β=98.51(3) °, V=2.9276 nm3, Z=2. 配合物中有两个CF3COO-基团与七配位Mn2中心相连, 其中一个为单齿配体, 另一个是双齿配体. 直流磁化率研究结果表明, 该配合物具有较高的自旋基态, 而交流磁化率依赖于外场频率变化极值的出现表明该配合物是一种单分子磁体.     

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。     

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.     

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.     

Effects of 3d-4f magnetic exchange interactions on the dynamics of the magnetization of Dy(III)-M(II)-Dy(III) trinuclear clusters

[{Dy(hfac)(3)}(2){Fe(bpca)(2)}] x CHCl(3) ([Dy(2)Fe]) and [{Dy(hfac)(3)}(2){Ni(bpca)(2)}]CHCl(3) ([Dy(2)Ni]) (in which hfac(-)=1,1,1,5,5,5-hexafluoroacetylacetonate and bpca(-)=bis(2-pyridylcarbonyl)amine anion) were synthesized and characterized. Single-crystal X-ray diffraction shows that [Dy(2)Fe] and [Dy(2)Ni] are linear trinuclear complexes. Static magnetic susceptibility measurements reveal a weak ferromagnetic exchange interaction between Ni(II) and Dy(III) ions in [Dy(2)Ni], whereas the use of the diamagnetic Fe(II) ion leads to the absence of magnetic exchange interaction in [Dy(2)Fe]. Dynamic susceptibility measurements show a thermally activated behavior with the energy barrier of 9.7 and 4.9 K for the [Dy(2)Fe] and [Dy(2)Ni] complexes, respectively. A surprising negative effect of the ferromagnetic exchange interaction has been found and has been attributed to the structural conformation of these trinuclear complexes.     

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.     

Ferromagnetic versus antiferromagnetic exchange interactions in tetrathiafulvalene-based 3d/4f heterobimetallic complexes

(TTF-salphen)M compounds (TTF-salphen(2-)=4,5-bis(propylthio)tetrathiafulvalene-N,N'-phenylenebis(salicylideneimine) dianion; M=Cu(II) and Ni(II)) have been treated with Ln(hfac)(3)·2H(2)O precursors (hfac(-)=1,1,1,5,5,5-hexafluoroacetylacetonate anion; Ln=Gd(III), Tb(III), and Dy(III)) to elaborate unprecedented 3d/4f TTF-based heterobimetallic complexes of formula [(TTF-salphen)MLn(hfac)(3)]. All the structures of these compounds have been resolved by X-ray diffraction on single crystals. The structures of these complexes are formed by a TTF-salphen(2-) ligand coordinated to the 3d metal ions in the inert tetradentate N(2)O(2) site. The Ln(hfac)(3) fragment is coordinated to the (TTF-salphen)M one through the two phenolate bridges. Even if the complexes are similar in both Cu(II) and Ni(II) families, the crystal packing is different. In the first case, dimers of TTF-salphen(2-) donors constitute the organic network. In the other case, a reminiscent organic network is observed with S···S contacts. The photophysical properties of [(TTF-salphen)CuDy(hfac)(3)] (3) in chloroform solution highlight the redshift of the TTF→salphen charge transfer (400 cm(-1)) relative to the analogue excitations in (TTF-salphen)Cu, which attest to the stability of these structures in solution. Static magnetic measurements have allowed us to quantify the ferromagnetic interactions (J=+1.29 cm(-1)) between Cu(II) and Gd(III) in the [(TTF-salphen)CuGd(hfac)(3)] complex. Finally, an empirical method that consists of the comparisons of the magnetic properties of [(TTF-salphen)CuTb(hfac)(3)] with [(TTF-salphen)NiTb(hfac)(3)] and [(TTF-salphen)CuDy(hfac)(3)] with [(TTF-salphen)NiDy(hfac)(3)] has established that ferromagnetic interactions take place between Cu(II) and Tb(III) ions, whereas unusual antiferromagnetic interactions have been identified between Cu(II) and Dy(III) ions.     

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.