Studies on Magnetic Properties of Transition Metal Polynuclear Complexes and Molecular Design Aiming to Single-Molecule Magnets

1.单链磁体的弛豫机理单链磁体是由单分子磁体发展而来的一类量子磁体。基于自旋矢量模型，提出了一种新的自旋-矢量模型，该模型的特征是链内铁磁相互作用J和单离子各向异性D。该模型可以应用于从孤立分子的SMM极限J/D0到纯伊辛链的Glauber动力学极限J/D&gt；&gt；1的多种SCM体系。该模型的一个很好的特点是，它合理地解释了在一些铁磁SCM中观察到的“势垒高度交叉”，它是从具有不同激活势垒的单自旋翻转到双自旋团簇翻转的主导弛豫过程的交叉。2.自旋交叉络合物[Mn(TAA)]自旋交叉络合物[Mn(TAA)]的临界现象被认为是除了光学可控的自旋双稳外还表现出介电响应的独特体系。为了弄清导致[Mn(TAA)]晶体相变的分子间相互作用，我们制备了与[Ga(TAA)]的混晶，[Ga(TAA)]是具有同构晶体结构的锰络合物的抗磁性类似物。由磁测量和介电测量确定的[MnxGa；lt；1-x&gt；(TAA)]的T-x相图揭示了从一级相变到自旋平衡行为的临界现象。自旋交叉相变的抑制使得估算[Mn(TAA)]分子的假旋转能垒成为可能。3.磁化分析计算机程序的开发开发了一些计算机程序来分析SMM的磁化曲线和HF-EPR结果。其中，实现配位场理论方法的程序特别有效地解释了包括Co(II)离子在内的SMM的磁性，这是传统的自旋-哈密顿方法难以处理的。

1.Relaxation Mechanism of Single-Chain MagnetsSingle-Chain Magnets (SCMs) are a class of quantum magnets, recently developed from Single-Molecule Magnets (SMMs). We proposed a novel mechanism of relaxation processes in SCMs based on a spin-vector model characterized by an intrachain ferromagnetic interaction J along with a single-ion anisotropy D. This model can be applied to a wide range of SCM systems from a SMM limit J/D 0 of isolated molecule to a Glauber-dynamics limit J/D >> 1 for a pure Ising chain. It is an excellent feature of the model that it provides a rational account for a "barrier-height crossover" observed in some ferromagnetic SCMs as a crossover of dominant relaxation process from a single-spin flip to a two-spin cluster flip possessing different activation barriers.2.Critical Phenomena of Spin-Crossover Complex [Mn(taa)]Spin-crossover complex [Mn(taa)] is known as a unique system showing a dielectric response in addition to an optically-controllable spin bistability. In order to clarify intermolecular interactions responsible to the phase transition in [Mn(taa)] crystals, we prepared some mixed-crystals with [Ga(taa)], a diamagnetic analogue of the Mn complex with the isomorphous crystal structure. A T-x phase diagram of [Mn_xGa_<1-x>(taa)] determined by magnetic and dielectric measurements revealed a critical phenomenon switching from a first-order phase transition to a spin-equilibrium behavior. The suppression of the spin-crossover phase transition made it possible to estimate the energy barrier for pseudo-rotation of an [Mn(taa)] molecule.3.Development of Computer Programs for Magnetization AnalysisSome computer codes were developed to analyze magnetization curves and HF-EPR results of SMMs. Among them a code implementing the ligand-field theoretical approach was especially effective to elucidate magnetic properties of SMMs including Co(II) ions, which were difficult to be treated by conventional spin-Hamiltonian approach.