【作者】 陈少宏；

【导师】 何云；

【作者基本信息】 广西师范大学 ， 原子与分子物理， 2010， 硕士

【摘要】 分子磁体是以分子或离子为构件的一种新型的软材料,分子材料在临界温度以下有三维磁有序结构,它的磁相互作用主要来源于分子间的相互作用,近年来,材料科学的研究已成为化学家、物理学家研究的焦点,其制备常采用有机或无机化学合成方法。作为磁性材料,分子铁磁是具有磁学物理特征的分子基材料。当然,分子磁性材料具有体积小、相对密度轻、结构多样化、易于复合加工的特点,涉及化学、物理、材料和生命科学等诸多学科的新成型的研究领域,它有可能成为制作航天器、微波吸收隐身、电光交叉等应用领域材料。主要研究具有磁性、磁性与光学或电磁屏蔽和信息存储的材料。我们认为对于分子磁性的研究仍然处于理论探索研究阶段。本论文主要研究的是用草酸根作为桥联配体的分子磁体的磁性研究。草酸根是一种能够很有效的传递磁性离子之间的相互作用的桥联配体,而且草酸根的对称性和反对称性展现出配合物具有丰富的磁性质特点。草酸根配体的长度很小,作用力很强容易形成双桥链,这增加了磁交换途径,使磁性增强,居里点增高。它是很有实际应用价值的桥联配体。通过穆斯保尔谱学的测量,我们能够得到样品的超精细磁场、自旋态、金属离子的价态等性质。在完成论文的过程中,我们得到以下几个主要研究结果：1.在化合物NBu4Zn(Ⅱ)nFe(Ⅱ)1-n[Fe(Ⅲ)(ox)3]系列中,对于0＜n≤0.1化合物的磁化率和磁化强度被研究,通过量子磁性测量仪测量,化合物在2-290K范围内低于35K时化合物存在自旋玻璃态,在场冷的情况下,在0≤n≤0.08化合物在32-41.5K的范围内存在两个温度补偿点,在系列材料中,我们发现多磁极翻转现象。我们用亚铁磁分子场理论给予解释。对n≥0.1温度补偿点和自旋玻璃态消失,n的大小影响着温度补偿点和自旋玻璃态。2.合成了化合物NBu4FeⅡxMnⅡ1-x[FeⅢ(OX)3]系列,系列化合物的磁相变温度Tc变化说明了掺杂对物质磁相互作用有影响,在低温范围内系列物质表现出很强的反铁磁性,且出现较弱的自旋倾斜现象。磁性测量结果表明在Fe(Ⅲ)(d5,e2gt32g,S=5/2)和Mn(Ⅱ)(d5,e2gt32g,S=5/2)之间发生的反铁磁性超交换相互作用和在Fe(Ⅲ)(d5,e2gt32g,S=5/2)和Fe(Ⅱ)(d6e2gt42g,S=2)之间发生的反铁磁性超交换相互作用。3.合成了配合物{[N(n-C4H9)4][FeFe(C2O4)3]}。。我们用常温穆斯保尔谱研究证明,在该配合物中存在Fe3+(d5,e2gt32g,S=5/2)态、Fe2+(d6,e2gt42g,S=2)态和Fe2+(d6,t62g,S=0)态。最后,总结了本文的工作,并展望了未来草酸根分子磁体的研究方向。更多还原

【Abstract】 Molecule-based magnets which molecules or ions act as a building blocks is a new type of soft magnetic material. Molecule-based materials have a three-dimensional structure of magnetic ordering below transition temperature. Its magnetic internation derived from intermolecular interactions. In recent years, the research of materials science has become the focus of chemists and physicists, It was prepared to use synthesis of organic or inorganic chemical. As a magnetic material, molecular ferromagnet is a magnetic physical characteristics of the molecule-based materials. Certainly, molecular magnetic materials is the characteristics of a small bulk, the relative density light, the structural diversification, the easy-to-composite processing. It was related to chemistry, physics, material, life sciences, and many other domain, formed a new field of study. It may become a production materials of space vehicle, microwave absorbing stealth, electro-optical applications and so on. Major study is possessed of materials of magnetic, magnetic and optical, electromagnetic shielding and information storage. We believe that the study of molecular magnetism lies the stage of the theoretical exploration yet.In this paper, we mainly study that focus on is the root of oxalic acid as a bridging ligand of the magnetic properties of molecular magnets.The oxalate group has been shown to be an excellent bridging ligand in supporting the magnetic exchange interaction. Symmetry and anti-symmetry of oxalate show the rich features nature of the complex,the length of oxalate ligand is small. This increases the magnetic exchange, magnet and Curie point strongly,It is very practical value of the bridging ligand. By Mossbauer spectroscopy measurements, We can reach samples of the hyperfine magnetic field, spin state, metal ion valence state and other properties.During the completion of the course paper, we have reached the following some key findings1. The temperature dependence of the molar magnetic susceptibility and magnetization of NBu4Zn(Ⅱ)nFe(Ⅱ)1-n[Fe(Ⅲ)(ox)3 compounds with 0< n≤0.1 was studied in the temperature range of 2-290K. In the FC mode, the compounds with 0≤n≤0.08 showed two temperature compensation points on temperature scale in 32-41.5K temperature range. Multiple magnetic-pole reversals were observed in the material. We can explain the observed multiple magnetic-pole reversals in terms of a combination of molecular-field theory and the coercive field. n≥0.1, the temperature compensation point disappeared. At the same time, we found spin glass state below 35K range.2. Some materials of general molecular formula NBu4FeⅡxMnⅡ1-x [FeⅢ(OX) 3] were synthesized, variation of magnetic phase transition temperature Tc of series of compounds illustrates the interaction of magnetic doping in the material. At low temperatures series of compounds show a strong anti-ferromagnetic and appears weaker spin-sloped phenomenon. Results of magnetic measurement show that the anti-ferromagnetic super-exchange interaction between Fe (Ⅲ) (d5, e2gt32g, S= 5/2) and Mn (II) (d5, e2gt32g, S = 5/2) and the anti-ferromagnetic super-exchange interaction between Fe (Ⅲ) (d5, e2gt32g, S = 5/2) and Fe (Ⅱ)(d6,e2gt42g,S= 2).3.{[N (n-C4H9) 4] [FeFe (C204) 3]}n was synthesized, we study it with MOssbauer spectrum in the room temperature. It proved that the compound existed high-spin Fe (Ⅲ) (d5, e2gt32g, S= 5 /2), high-spin Fe (II) (d6, e2gt42g, S= 2) and low spin Fe (II) (d6, t62g, S= 0).Eventually, this article summarizes the work and looked to the future of molecular magnets oxalate research direction更多还原