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在单分子磁体基础上发展起来的一类量子磁体。我们提出了一种基于链内铁磁相互作用J和单离子各向异性D的自旋矢量模型的SCM弛豫过程的新机制，该模型可以应用于广泛的SCM系统，从孤立分子的SMM极限J/D 0到纯Ising链的glauber动力学极限J/D >> 1。该模型的一个重要特点是，它合理地解释了在某些铁磁SCMs中观察到的“势垒高度交叉”，即从具有不同激活势垒的单自旋翻转到具有不同激活势垒的双自旋簇翻转的主导弛豫过程的交叉。自旋交叉配合物[Mn(taa)]是一种独特的系统，除了具有光学可控的自旋双稳定性外，还具有介电响应。为了弄清[Mn(taa)]晶体中导致相变的分子间相互作用，我们制备了一些与[Ga(taa)]混合的晶体，这是一种具有同晶结构的Mn配合物的抗磁性类似物。由磁和介电测量测定的[Mn_xGa_<1-x>(taa)]的T-x相图揭示了从一阶相变到自旋平衡行为转换的临界现象。抑制自旋交叉相变使得估计[Mn(taa)]分子伪旋转的能垒成为可能。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，实现配体场理论方法的代码特别有效地解释了含Co（II）离子的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.