Ultrafast spin dynamics in molecular magnets

分子磁体中的超快自旋动力学

• 批准号: EP/S018824/1
• 负责人: Johan Johansson
• 金额: $ 32.83万
• 依托单位: University of Edinburgh
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2019
• 资助国家: 英国
• 起止时间: 2019 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FS018824%2F1
• 关键词: Ultrafast; spin; dynamics; molecular; magnets

Magnetic materials have completely changed how we can access and make use of information during the last century. Digital information is stored in hard-drives in magnetic domains, where the north and south poles represent binary "one" and "zero". How fast data can be recorded is limited to the rate at which the poles of these domains can be reversed. Recent advances using laser pulses as short as a millionth billionth of a second (or femtosecond) have made it possible to overcome this limitation by switching magnetic domains 1000 times faster than what current technology can achieve. Ultrafast magnetism therefore has the potential to drastically increase the rate of writing information to memories by orders of magnitude and is one of the frontiers in current magnetic research. A continued development of new magnetic materials and new ways of controlling them will ensure that we can make the most of large data sets, which in turn will improve many aspects of our lives such as health care, government, logistics and will reduce global energy consumption.Another development, but hitherto unexplored in the context of ultrafast magnetism, is the study of molecular magnets. These will overcome the problems with reducing the size of data bits in hard drives to that of a few atoms, where the materials currently used have reached their size limit. Besides from reducing the size, molecular magnets also show another advantage for ultrafast magnetism. It has recently been shown that magnetic materials with localised magnetic moments are promising for achieving fast magnetisation reversal. These systems can be switched much faster in a process that generates less heat. Since the magnetic ordering of molecular magnets are from localised magnetic moments, these systems are very promising because their chemical flexibility makes it is possible to tune the interaction between the localised moments, and more importantly, their response to light perturbation. This will allow us to develop nanomaterials that can be switched using ultrashort laser pulses.In this proposal, we will look at a series of model compounds, where it is possible to systematically change the elemental composition and stoichiometry of the materials to tune their magnetic and optical properties. In particular, the project will be split into two work packages (WPs): spin-flips in Prussian Blue Analogues (WP1) and dynamics of photomagnets (WP2). In WP1, Prussian blue analogues (PBAs) will be studied. It is known that very fast spin-flips can happen in these materials after light excitation. We have recently applied specialised methods to directly observe the spin-flip on a femtosecond timescale. We will extend these methods to a range of PBAs to increase our understanding of how the interaction between the magnetic moments govern the dynamics after the spin-flip on the localised sites. In WP2, we will build on this knowledge and study a similar system based on Fe and Nb. After light excitation, the initially diamagnetic (or "non-magnetic") Fe(II) centres are switched, in a similar process to what was described earlier, but in this case, the spin-excited state is trapped after photoexcitation. This leads to a magnetic interaction between paramagnetic Nb centres and eventually a macroscopic magnetic ordering takes place. It is not known how fast the magnetic ordering process takes place, however, our methods can measure this with unprecedented time resolution. This will allow us to understand the mechanisms for the magnetic switching process, which is necessary for optimising the process to incorporate both the materials and techniques in a future ultrafast and ultradense magneto-optical data storage devices. EPSRC Reference: EP/S018824/1

在上个世纪，磁性材料彻底改变了我们获取和利用信息的方式。数字信息存储在磁域的硬盘驱动器中，在磁域中，北极和南极代表二进制“1”和“0”。记录数据的速度受限于这些域的极点可以反转的速度。最近使用短至百万亿分之一秒(或飞秒)的激光脉冲的进步使人们有可能通过以比当前技术所能实现的速度快1000倍的速度来切换磁域来克服这一限制。因此，超快磁性有可能极大地提高向存储器写入信息的速度，并以数量级的速度增长，是当前磁性研究的前沿之一。新的磁性材料和控制它们的新方法的持续发展将确保我们能够最大限度地利用大数据集，这反过来将改善我们生活的许多方面，如医疗保健、政府、物流，并将减少全球能源消耗。另一项发展，但迄今未在超快磁性的背景下探索，是对分子磁体的研究。这些将克服将硬盘驱动器中数据比特的大小减少到几个原子大小的问题，在这些原子中，目前使用的材料已经达到其大小限制。除了减小尺寸外，分子磁体还显示出超快磁性的另一个优势。最近的研究表明，具有局域磁矩的磁性材料有望实现快速磁化反转。在产生较少热量的过程中，可以更快地切换这些系统。由于分子磁体的磁序来自定域磁矩，这些系统非常有希望，因为它们的化学灵活性使调节定域磁矩之间的相互作用成为可能，更重要的是，它们对光扰动的反应。这将使我们能够开发可以使用超短激光脉冲进行开关的纳米材料。在这项提议中，我们将研究一系列模型化合物，其中有可能系统地改变材料的元素组成和化学计量比，以调节它们的磁性和光学性能。特别是，该项目将被分成两个工作包(WP)：普鲁士蓝类似物的自旋翻转(WP1)和光磁体的动力学(WP2)。在WP1中，将研究普鲁士蓝类似物(PBAS)。众所周知，在光激发后，这些材料中会发生非常快的自旋翻转。我们最近应用了专门的方法来直接观测飞秒时间尺度上的自旋翻转。我们将把这些方法扩展到一系列PBA，以增加我们对局域位置上自旋翻转后磁矩之间的相互作用如何控制动力学的理解。在WP2中，我们将建立在这些知识的基础上，研究基于Fe和Nb的类似系统。在光激发后，最初的抗磁(或非磁性)Fe(II)中心被切换，这与前面描述的过程类似，但在这种情况下，自旋激发态在光激发后被俘获。这导致了顺磁Nb中心之间的磁相互作用，并最终发生了宏观磁有序。目前尚不清楚磁性有序过程发生的速度有多快，然而，我们的方法可以以前所未有的时间分辨率测量这一过程。这将使我们了解磁开关过程的机制，这是优化该过程以将材料和技术纳入未来超快和超高密度磁光数据存储设备所必需的。EPSRC参考文献：EP/S018824/1

项目成果

Transient magneto-optical spectrum of photoexcited electrons in the van der Waals ferromagnet Cr 2 Ge 2 Te 6

范德华铁磁体 Cr 2 Ge 2 Te 6 中光激发电子的瞬态磁光光谱

• DOI: 10.1103/physrevb.107.174432
• 发表时间: 2023
• 期刊: Physical Review B
• 影响因子: 3.7
• 作者: Sutcliffe E

Preparation of thin films of molecule-based magnets for optical measurements

用于光学测量的分子磁体薄膜的制备

• DOI: 10.1016/j.tsf.2021.138767
• 发表时间: 2021
• 期刊: Thin Solid Films
• 影响因子: 2.1
• 作者: Lewis H

Towards understanding and controlling ultrafast dynamics in molecular photomagnets

• DOI: 10.1016/j.ccr.2023.215346
• 发表时间: 2023
• 期刊: Coordination Chemistry Reviews
• 影响因子: 20.6
• 作者: T. Penfold;J. Johansson;Julien Eng

A Hybrid Magneto-Optic Capacitive Memory with Picosecond Writing Time

• DOI: 10.1002/adfm.202212173
• 发表时间: 2023-01-20
• 期刊: ADVANCED FUNCTIONAL MATERIALS
• 影响因子: 19
• 作者: Rogers，Matthew;Habib，Ahasan;Cespedes，Oscar
• 通讯作者: Cespedes，Oscar

A Femtosecond Magnetic Circular Dichroism Spectrometer

飞秒磁圆二色性光谱仪

• DOI: 10.48550/arxiv.2107.10729
• 发表时间: 2021
• 作者: Sutcliffe J