The Effect of High Pressure on Single Molecule Magnets

磁性材料的应用范围很广，包括信息存储设备，其中信息存储在金属氧化物或合金的磁性颗粒中。为了在给定大小的磁盘驱动器或长度的磁带上增加可以存储的信息量，有一种驱动器可以用越来越小的颗粒制造设备。存在某些过渡金属配合物，其核心包含由配体分子衍生的氧原子和氮原子连接的金属离子。其中一些复合物属于一类称为单分子磁铁的分子。单分子磁体的行为就好像是包裹在有机配体鞘中的很小的金属氧化物碎片。这些碎片比目前用于信息存储的氧化物颗粒要小得多，因此它们可以代表一种实现尽可能高的信息存储密度的方法。每个分子代表一位信息：一种磁性状态可能代表二进制0，另一种则代表二进制1。单分子磁体的基本性质是引起强烈科学兴趣的课题。它们在很大程度上取决于用于形成络合物的金属离子的性质、离子之间的距离以及连接金属中心的配体原子的角度。在以前的工作中，我们已经证明，施加1 - 100千巴的压力（大约是大气压力的1000到10万倍）可以改变原子间的几何形状。这些压力是通过在两个金刚石砧之间压缩样品来实现的，这种装置可以很容易地放入手掌中。我们还可以通过x射线晶体学确定单分子磁体的结构，并测量它们在金刚石砧胞内高压时的磁性能。因此，我们可以以一种非常有控制和系统的方式，探测几何形状的变化对给定复合物的结构和磁性的影响。这些实验将是独一无二的，任何地方都没有其他合作团队拥有制造单分子磁铁的综合专业知识，建立合适的高压电池，并研究高压下复合物的结构和磁性。我们将从研究高压对一些简单的复合体和一些已知的单分子磁体的影响开始，建立对新分子的研究。这项研究的结果不仅具有重大的基础意义，使磁性能的变化与结构变化密切相关，而且还可能揭示将磁性非活性分子转化为单分子磁体所必需的结构变化。

Magnetic materials are used in a broad range of applications, including devices for information storage, in which information is stored by magnetic particles of metal oxide or alloys. There is a drive to make devices with ever-smaller particles in order to increase the amount of information that can be stored on a given size of disk-drive or length of magnetic tape. Certain transition metal complexes exist which consist of a core containing metal ions connected by oxygen and nitrogen atoms derived from ligand molecules. Some of these complexes fall into a class of molecules called Single Molecule Magnets. Single molecule magnets behave as though they are very small fragments of metal oxide encapsulated within a sheath of organic ligands. These fragments are much smaller than the oxide particles currently used in information storage, and therefore they could represent a means of achieving the highest possible density of information storage. Each molecule would represent a single bit of information: one magnetic state might represent a binary 0, the alternative a binary 1.The fundamental properties of single molecule magnets are the subject of intense scientific interest. They are strongly dependent on the nature of the metal ions used to form the complex, the distances between the ions, and the angles subtended at the ligand atoms which link the metal centres together. In previous work, we have shown that interatomic geometry can be altered by applying pressures of 1 - 100 kbar, that is about 1000 to 100 000 times atmospheric pressure. These pressures are achievable by compressing a sample between two diamond anvils in devices which would fit readily into the palm of one's hand. We can also determine the structures of the single molecule magnets by X-ray crystallography, and measure their magnetic properties, while they are at high pressure inside the diamond anvil cell. We can therefore probe, in a very controlled and systematic way, the effect that changes in geometry have on structural and magnetic properties of a given complex.These experiments will be unique, no other collaborative team anywhere has the combined expertise to make single molecule magnets, build suitable high pressure cells and investigate the structures and magnetic properties of the complexes at high pressure. We will begin by investigating the effect of high pressure on some simple complexes and on some well-known single molecule magnets, building up towards investigations of new molecules. The results of this research will not only be of great fundamental interest, enabling changes in magnetic properties to be closely correlated with structural changes, but they may also reveal the structural changes necessary to convert magnetically inactive molecules into single molecule magnets.