Nanochemistry and magnetism

An analysis of magnetism of nanochemical systems opens up new ways to creating ferromagnets from diamagnetic substances and new principles for constructing molecular ferromagnets, hybrid magnetic materials, and monomolecular magnets on the basis of high-spin molecules and complexes. Their use in spin computing is considered.     

Design of molecular ferromagnets

A large variety of molecular ferromagnets have been synthesized since the discovery of the first organic ferromagnets, including pure organic compounds, organometallic charge-transfer complexes, metal complex-organic radical compounds, and transition metal complexes coupled to organic radicals. Besides, there are many reports on the observation of ferromagnetism in polymers and organic matrix composites. Molecular ferromagnets have great potential in different areas of technology such as low frequency magnetic shielding, magnetic imaging, magneto-optics and information storage. We provide a brief review on the current strategies for the design of molecular (organic) ferromagnets. This includes exploiting the inherent advantages of molecular systems, such as the ability to fine-tune the properties at the molecular level, and to control dimensionality, supramolecular structuring and hierarchy of spin interactions etc. for carrying out structural modifications and chemical functionalisations of stable open-shell molecules in order to generate supramolecular structures in which the natural prediction for antiparallel spin alignment (antiferromagnetism) is avoided.     

一种设计实用分子铁磁体的有效构件——普鲁士蓝类配合物

合成常温下的分子铁磁体是化学家研究的新领域。普鲁士蓝类分子铁磁体是目前最有望用于实际的一类体系。我们拟就该类配合物的设计、合成及磁性特点作一展望性评述。     

无机类分子性铁磁体的设计

分子性铁磁体的设计及合成是当今化学界的热点课题之一，无机类分子性铁磁体是一类重要的分子性铁磁体。本文论述这类分子性磁体的设计途径以及最新研究进展。     

Physicochemical foundations of synthesis of new ferromagnets from chalcopyrites A<Superscript>II</Superscript>B<Superscript>IV</Superscript>C<Stack><Subscript>2</Subscript><Superscript>V</Superscript></Stack>

The results of studying phase equilibria of ternary A^IIB^IVC^V systems have been reported. Physicochemical foundations have been developed for the synthesis of new ferromagnets with Curie temperatures above room temperature structurally compatible with basic semiconducting materials. Methods of synthesis and physicochemical properties of manganese-doped A^IIB^IVC₂^V ferromagnets have been described. The results of theoretical simulation of magnetic properties have been considered and basic approaches to the explanation of the emergence of ferromagnetism in A^IIB^IVC₂^V doped with 3d metals have been surveyed. The most promising ways to produce and study dilute magnetic semiconductors as spintronics materials have been presented.     

有机高分子磁性体的进展

本文介绍近年来,结构型有机高分子磁性体研究所取得的进展,包括磁性体简单的设计原理、含金属原子和不含金属原子的磁性体、磁性体模型的制备以及可能应用的前景。     

Framework-structured weak ferromagnets

Framework-structured weak ferromagnets are new rising stars in molecule-based magnetic materials. The framework structures are powerful carriers for long-range ordering of spins. And weak ferromagnetism due to spin canting is an effective approach for magnets because of its frequent occurrence and desired spontaneous magnetization as long as the canting angle γ is large enough. In this critical review, we provide an overview of the various framework-structured weak ferromagnets based on different grades of ligands (from mono-atom to three-atom-like ligands). Particular emphasis is given to the relationships between structural features and the properties, rational employment of the ligands, and weak ferromagnetic strategies for molecule-based magnets with exciting properties and applications (273 references).     

Molecular and Crystal Magnetic Engineering of Polymetallic Coupling System: From Magnetic Molecules to Molecular Magnets

One of the main challenges in the field of molecular materials is the design of molecular ferromagnets. General design strategy includes two steps, that is molecular magnetic engineering and crystal magnetic engineering. The first step is the synthesis of ferromagnetically coupled polymetallic systems. The second step is the assembly of polymetallic systems with muti‐dimensional structure and exhibiting a ferromagnetic transition. This paper summarized the strategies of molecular design and crystal engineering allowed to obtain such systems and our efforts in the fields of molecular magnetism and molecular‐based magnets.     

Donor-Acceptor-Substituted Cyclic π-Electron Systems—Probes for Theories and Building Blocks for New Materials

Donor and acceptor substituents stabilize (4n)π-electron systems and destabilize those with (4n+2)π electrons. The same is true for the transition states of pericyclic reactions, which explains the appearance of dipolar intermediates in symmetry-allowed cycloadditions and sigmatropic rearrangements. Donor-acceptor-substituted semibullvalenes undergo rapid Cope rearrangement, as do tetraazabarbaralanes. In contrast, tetraazasemibullvalenes can not be isolated, since the isomeric tetrazocines always result. The usefulness of the donor-acceptor concept in preparative chemistry is demonstrated by numerous stable cyclic (4n)π-electron systems, like donor-acceptor-substituted cyclobutadienes, tetraaminobenzene, and p-benzoquinone dications, benzodiazepinyl anions, and donor-acceptor-substituted cyclopentadienyl cations and their heteroatom-containing analogues. The new compounds are of interest in the fields of organic metals and ferromagnets, nonlinear optics, and dyestuffs, among others.     

Development of minimized mixing molecular orbital method for designing organic ferromagnets

Predicting the high spin stability of organic radicals correctly for designing organic ferromagnets remains a significant challenge. We have developed a method with an index (L_min) for predicting the high spin stability of conjugated organic radicals at the restricted open‐shell Hartree–Fock level. Unitary transformations were performed for localizing the coefficients of nonbonding molecular orbitals, and subsequently the localized coefficients were used to calculate L_min that indicates the high spin stability of conjugated organic radicals. This method can be combined with the elongation method to treat huge high spin open‐shell systems. Thus, this method is useful for designing organic ferromagnets. © 2015 Wiley Periodicals, Inc.     

超级材料--高维分子基铁磁体的设计与合成

高维分子基铁磁体的设计与合成是自然界向化学家的挑战。本文在简述了高维分子基铁磁体的重要性后,侧重介绍了设计与合成高维磁体的常用桥基、合成方法以及最新研究进展。     

Spintronics: a challenge for materials science and solid-state chemistry

Spintronics is a multidisciplinary field involving physics, chemistry, and engineering, and is a new research area for solid-state scientists. A variety of new materials must be found to satisfy different demands. The search for ferromagnetic semiconductors and stable half-metallic ferromagnets with Curie temperatures higher than room temperature remains a priority for solid-state chemistry. A general understanding of structure-property relationships is a necessary prerequisite for the design of new materials. In this Review, the most important developments in the field of spintronics are described from the point of view of materials science.     

Vanadium--benzimidazole-modified sDNA: a one-dimensional half-metallic ferromagnet

We perform investigations on the structural, electronic, and magnetic properties of vanadium-stacked benzimidazole-modified single-stranded DNA (sDNA) using density functional theory. We find that the vanadium atoms aligned along the helical axis interact ferromagnetically. Furthermore, under the influence of an external electric field, these one-dimensional ferromagnets show half-metallic behavior, with the closing of the spin gap in the minority spin channel. The half-metallic behavior of these systems crucially depends on the hybridization of the vanadium valence orbitals in the stacking direction. Also, we show that the sugar-phosphate backbone does not influence the magnetic interactions, making the modified sDNA scaffold ideal for advanced spintronics applications.     

Magnetic anisotropy in a heavy atom radical ferromagnet

High-field, single-crystal EPR spectroscopy on a tetragonal bisdiselenazolyl ferromagnet has provided evidence for the presence of easy-axis magnetic anisotropy, with the crystallographic c axis as the easy axis and the ab plane as the hard plane. The observation of a zero-field gap in the resonance frequency is interpreted in terms of an anisotropy field several orders of magnitude larger than that observed in light-heteroatom, nonmetallic ferromagnets and comparable (on a per-site basis) to that observed in hexagonal close packed cobalt. The results indicate that large spin-orbit-induced magnetic anisotropies, typically associated with 3d-orbital-based ferromagnets, can also be found in heavy p-block radicals, suggesting that there may be major opportunities for the development of heavy p-block organic magnetic materials.     

Magnetic and spectroscopic properties of benzylammomium tetrahalogenochromates(II) containing mixed halides (Cl and Br)

Summary The complexes [PhCH₂NH₃]₂[CrCl_xBr_4–x], x=0, 1, 1.8, 3.3 or 4, have been prepared, and the new mixed halides characterised by magnetic and spectroscopic measurements. They are further examples of two dimensional ferromagnets. The magnitude of the magnetic interaction increases slightly with replacement of chloride by bromide.     

Metal bis-1,2-dithiolene complexes in conducting or magnetic crystalline assemblies

Crystalline materials studied for their conducting or magnetic properties based on metal complexes of 1,2-dithiolene ligands are discussed emphasising the wide diversity of ligands now available and the variety of materials prepared from these. Complexes have been prepared using electronically delocalised dithiolene ligands where the core complex is extended with units such as thioethers, aromatics, tetrathiafulvalene (TTF) and other heterocycles to explore the influence of these variations on the solid-state structures and properties derived from them. Although superconductivity in dithiolene complexes has so far been limited to [M(dmit)₂]^X− salts, other ligand systems have given rise to numerous conducting and metallic salts and have proven informative in rationalising the criteria for design of the molecular units. Novel material properties have been observed in systems such as hybrid conducting ∣ magnetic materials and mixed dithiolene-metallocene salts. In particular, highly conducting and metallic single-component materials have recently been found uniquely within materials based on metal-bis-1,2-dithiolene complexes. Magnetic materials containing dithiolene-complex building blocks have yielded systems such as ferromagnets, ferrimagnets, metamagnets and spin ladders in addition to other model systems suitable for the study of magnetic ordering. These can involve systems where the dithiolene complex is the only paramagnetic component in addition to more complex systems involving other types of building block.     

几种纤锌矿相半金属铁磁体磁学性能的第一原理研究

通过基于密度泛函理论的第一原理计算,优化了纤锌矿结构的化合物TmZn15S16(Tm=V,Cr,Mn)的几何结构,并研究了它们的磁学性能.结果表明:TmZn15S16均为典型的半金属铁磁体,它们的超胞磁矩分别为3.0099μB,3.9977μB和5.0092μB;这些磁矩主要来源于被掺入的过渡元素;CrZn15S16的半金属特性比VZn15S16和MnZn15S16更稳定;这些半金属铁磁体的半金属带隙均比较宽,表明它们可能具有较高的居里温度;TmZn15S16中杂质过渡离子的电子结构分别为V:eg2↑t12g↑,Cr:eg2↑t22g↑和Mn:eg2↑t32g↑.     

Ferromagnetism and chirality in two-dimensional cyanide-bridged bimetallic compounds

The combination of hexacyanoferrate(III) anions, [Fe(CN)(6)](3)(-), with nickel(II) complexes derived from the chiral ligand trans-cyclohexane-1,2-diamine (trans-chxn) affords the enantiopure layered compounds [Ni(trans-(1S,2S)-chxn)(2)](3)[Fe(CN)(6)](2).2H(2)O (1) and [Ni(trans-(1R,2R)-chxn)(2)](3)[Fe(CN)(6)](2).2H(2)O (2). These chiral systems behave as ferromagnets (T(c) = 13.8 K) with a relatively high coercive field (H(c) = 0.17 T) at 2 K. They also exhibit an unusual magnetic behavior at low temperatures that has been attributed to the dynamics of the magnetic domains in the ordered phase.     

Constructing magnetic molecular solids by employing three-atom ligands as bridges

The combination of some three-atom bridges with paramagnetic 3d transition metal ions results in the systematic isolation of molecular magnetic materials, ranging from single-molecule and single-chain magnets to layered weak ferromagnets and three-dimensional porous magnets. The design strategy and role of secondary components, such as co-ligands, templates and other mixed short ligands are discussed.     

Magnetic properties of structurally organized sodium ferrophenylsiloxane

The Mösbauer spectrum and magnetic properties of individual sodium ferrophenylsiloxane were studied. Peculiar magnetic organization of iron metal oxide clusters in this compound was established. The cluster spin (9/2) is a result of antiferromagnetic compensation of four Fe ions with simultaneous parallel spin alignment of the other two Fe ions. This makes sodium ferrophenylsiloxane a promising base for the design of molecular ferromagnets.