Craig Gavin A, Sarkar Arup, Woodall Christopher H, Hay Moya A, Marriott Katie E R, Kamenev Konstantin V, Moggach Stephen A, Brechin Euan K, Parsons Simon, Rajaraman Gopalan, Murrie Mark
WestCHEM , School of Chemistry , University of Glasgow , Glasgow , G12 8QQ , UK . Email:
Department of Chemistry , Indian Institute of Technology Bombay , Powai , Mumbai , Maharashtra 400 076 , India . Email:
Chem Sci. 2017 Dec 19;9(6):1551-1559. doi: 10.1039/c7sc04460g. eCollection 2018 Feb 14.
Understanding and controlling magnetic anisotropy at the level of a single metal ion is vital if the miniaturisation of data storage is to continue to evolve into transformative technologies. Magnetic anisotropy is essential for a molecule-based magnetic memory as it pins the magnetic moment of a metal ion along the easy axis. Devices will require deposition of magnetic molecules on surfaces, where changes in molecular structure can significantly alter magnetic properties. Furthermore, if we are to use coordination complexes with high magnetic anisotropy as building blocks for larger systems we need to know how magnetic anisotropy is affected by structural distortions. Here we study a trigonal bipyramidal nickel(ii) complex where a giant magnetic anisotropy of several hundred wavenumbers can be engineered. By using high pressure, we show how the magnetic anisotropy is strongly influenced by small structural distortions. Using a combination of high pressure X-ray diffraction, methods and high pressure magnetic measurements, we find that hydrostatic pressure lowers both the trigonal symmetry and axial anisotropy, while increasing the rhombic anisotropy. The ligand-metal-ligand angles in the equatorial plane are found to play a crucial role in tuning the energy separation between the d and d orbitals, which is the determining factor that controls the magnitude of the axial anisotropy. These results demonstrate that the combination of high pressure techniques with studies is a powerful tool that gives a unique insight into the design of systems that show giant magnetic anisotropy.
如果数据存储的小型化要继续发展成为变革性技术，那么在单个金属离子层面理解和控制磁各向异性至关重要。磁各向异性对于基于分子的磁存储器至关重要，因为它将金属离子的磁矩沿易轴固定。器件将需要在表面沉积磁性分子，而分子结构的变化会显著改变磁性能。此外，如果我们要使用具有高磁各向异性的配位络合物作为更大系统的构建块，我们需要了解磁各向异性如何受到结构畸变的影响。在这里，我们研究了一种三角双锥镍（II）络合物，其中可以设计出几百波数的巨大磁各向异性。通过使用高压，我们展示了磁各向异性如何受到小的结构畸变的强烈影响。结合高压X射线衍射方法和高压磁测量，我们发现静水压力降低了三角对称性和轴向各向异性，同时增加了菱形各向异性。发现赤道平面中的配体 - 金属 - 配体角度在调节d和d轨道之间的能量分离方面起着关键作用，这是控制轴向各向异性大小的决定性因素。这些结果表明，高压技术与研究的结合是一种强大的工具，能为展示巨大磁各向异性的系统设计提供独特的见解。
