The link overlap and finite size effects for the 3D Ising spin glass

We study the link overlap between two replicas of an Ising spin glass in three dimensions using the Migdal-Kadanoff approximation and scaling arguments based on the droplet picture. For moderate system sizes, the distribution of the link overlap shows the asymmetric shape and large sample-to-sample variations found in Monte-Carlo simulations and usually attributed to replica symmetry breaking. However, the scaling of the width of the distribution, and the link overlap in the presence of a weak coupling between the two replicas are in agreement with the droplet picture. We also discuss why it is impossible to see the asymptotic droplet-like behaviour for moderate system sizes and temperatures not too far below the critical temperature. Received 25 May 1999     

基于席夫碱配体和两种苯甲酸盐构筑的两例Dy4配合物的合成、结构及单分子磁体性质

使用Dy (NO₃)₃·6H₂O与席夫碱配体2-(((2-羟基-3-甲氧基苄基)亚氨基)甲基)-4-甲氧基苯酚(H₂L)和2个辅助配体PhCO₂H和2-NO₂-PhCO₂H在乙醇中反应,得到2例Dy₄配合物[Dy₄(L)₄(PhCO₂)₂(NO₃)₂(EtOH)₂](1)和[Dy₄(L)₄(2-NO₂-PhCO₂)₂(NO₃)₂(EtOH)₂](2)。单晶X射线衍射解析表明配合物1和2均由Dy₂基本单元构建,形成中心对称的四核线性链状结构。配合物1和2中Dy₂单元中的一个Dy (Ⅲ)离子呈现七配位几何构型,另一个Dy (Ⅲ)离子呈现八配位几何构型。2例配合物均为单分子磁体,其能垒分别为110和108 K。通过理论计算对1和2的磁性能进行了分析。     

A Series of Novel Pentagonal-Bipyramidal Erbium(III) Complexes with Acyclic Chelating N3O2 Schiff-Base Ligands: Synthesis,Structure, and Magnetism

A series of six seven-coordinate pentagonal-bipyramidal (PBP) erbium complexes, with acyclic pentadentate [N₃O₂] Schiff-base ligands, 2,6-diacetylpyridine bis-(4-methoxybenzoylhydrazone) [H₂DAPMBH], or 2,6-diacethylpyridine bis(salicylhydrazone) [H₄DAPS], and various apical ligands in different charge states were synthesized: [Er(DAPMBH)(C₂H₅OH)Cl] (1); [Er(DAPMBH)(H₂O)Cl]·2C₂H₅OH (2); [Er(DAPMBH)(CH₃OH)Cl] (3); [Er(DAPMBH)(CH₃OH)(N₃)] (4); [(Et₃H)N]⁺[Er(H₂DAPS)Cl₂]⁻ (5); and [(Et₃H)N]⁺[Y₀.₉₅Er₀.₀₅(H₂DAPS)Cl₂]⁻ (6). The physicochemical properties, crystal structures, and the DC and AC magnetic properties of 1–6 were studied. The AC magnetic measurements revealed that most of Compounds 1–6 are field-induced single-molecule magnets, with estimated magnetization energy barriers, U_eff ≈ 16–28 K. The experimental study of the magnetic properties was complemented by theoretical analysis based on ab initio and crystal field calculations. An experimental and theoretical study of the magnetism of 1–6 shows the subtle impact of the type and charge state of the axial ligands on the SMM properties of these complexes.     

Large Spin‐Relaxation Barriers for the Low‐Symmetry Organolanthanide Complexes [Cp*2Ln(BPh4)] (Cp*=pentamethylcyclopentadienyl; Ln=Tb,Dy)

Single‐molecule magnets comprising one spin center represent a fundamental size limit for spin‐based information storage. Such an application hinges upon the realization of molecules possessing substantial barriers to spin inversion. Axially symmetric complexes of lanthanides hold the most promise for this due to their inherently high magnetic anisotropies and low tunneling probabilities. Herein, we demonstrate that strikingly large spin reversal barriers of 216 and 331 cm^?1 can also be realized in low‐symmetry lanthanide tetraphenylborate complexes of the type [Cp*₂Ln(BPh₄)] (Cp*=pentamethylcyclopentadienyl; Ln=Tb ( 1 ) and Dy ( 2 )). The dysprosium congener showed hysteretic magnetization data up to 5.3 K. Further studies of the magnetic relaxation processes of 1 and 2 under applied dc fields and upon dilution within a matrix of [Cp*₂Y(BPh₄)] revealed considerable suppression of the tunneling pathway, emphasizing the strong influence of dipolar interactions on the low‐temperature magnetization dynamics in these systems.     

Single-Molecule Magnets: Different Rates of Resonant Magnetization Tunneling in Mn12 Complexes

Two new molecular magnets , the dodecanuclear manganese complexes of the type [Mn₁₂O₁₂(O₂CR)₁₆(H₂O)₄] (known for R = CH₃, new for R = o-ClC₆H₄, o-BrC₆H₄) have contributed to a better quantum mechanical understanding of single-molecule magnets. For instance, appreciable differences in the steps seen in the magnetization hysteresis loops of these high-spin clusters are attributed to changes in the rates of magnetization tunneling from one complex to another.     

Two-Dimensional Nitroxide-Based Molecular Magnetic Materials

Manganese(II ) complexes of imidazolyl-substituted chelating nitronylnitroxides are characterized by a stereoselective arrangement of the metal centers and the ligands to give a honeycomblike layer structure (shown on the right). The magnetic properties at high temperature indicate the presence of a ferrimagnetic structure within the layers. At low temperatures, ferromagnetic ordering is observed.     

Single‐wall carbon nanotube interactions with copper‐oxamato building block of molecule‐based magnets probed by resonance Raman spectroscopy

The electronic interactions between the [Cu(opba)]²⁻ anions (where opba is orthophenylenebis (oxamato)) and single‐wall carbon nanotubes (SWCNTs) were investigated by resonance Raman spectroscopy. The opba can form molecular magnets, and the interactions of opba with SWCNTs can produce materials with very different magnetic/electronic properties. It is observed that the electronic interaction shows a dependence on the SWCNT diameter independent of whether they are metallic or semiconducting, although the interaction is stronger for metallic tubes. The interaction also is dependent on the amount of complex that is probably adsorbed on the carbon surface of the SWCNTs. Some charge transfer can be also occurring between the metallic complex and the SWCNTs. Copyright © 2012 John Wiley & Sons, Ltd.     

New chain polymer [Yb(tpa)(H2O)2Co(CN)6]n · 7n H2O: synthesis,structure, and magnetic characteristics

The 3d– 4f heterometallic polymeric complex, namely [Yb(tpa)(H₂O)₂Co(CN)₆]_n·7n H₂O [tpa = tris(2-pyridylmethyl)- amine], was synthesized and characterized. Its polymer structure is formed of [Yb(tpa)(H₂O)₂Co(CN)₆] chains and crystallization water molecules with a two-capped trigonal prism Yb³⁺ coordination polyhedron; the Yb³⁺ coordination number is 8, and the coordination site is YbN₆O₂. Magnetic characteristics indicate that the complex exhibits the properties of a single-chain magnet with a magnetization reversal barrier(!E/k_B) of 42 K.     

Synthesis of Isomeric Tb3+-Phthalocyanine Double-Decker Complexes Depending on the Difference in the Direction of Coordination Plane and Their Magnetic Properties

A C_4h symmetrically substituted phthalocyanine, 1,8,15,22-tertrakis(2,4-dimethylpent-3-oxy)phthalocyanine (H₂TdMPPc), was used to synthesize Tb³⁺-phthalocyanine double-decker complexes ([Tb(TdMPPc)₂]s). Because H₂TdMPPc has C_4h symmetry, S,S, R,R, and meso isomers of [Tb(TdMPPc)₂] were obtained depending on the difference in the direction of the coordination plane of two C_4h-type phthalocyanines with respect to a central Tb³⁺ ion. We investigated the physical properties of these [Tb(TdMPPc)₂] isomers, including their single-ion magnetic properties, and found that the spin-reversal energy barrier (U_eff) of the meso isomer was apparently higher than that of the enantiomers. Detailed crystal structural analyses indicated that the meso isomer has a more symmetrical structure than do the enantiomers, thereby suggesting that the higher U_eff of the meso isomer originated from the more highly symmetrical structure.     

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。