Advanced Characterisation of Magnetic Recording Media using Neutron Scattering

磁硬盘存储设备被发现在许多高科技系统的核心，我们认为理所当然的现代生活。作为计算机、现代视频存储设备和mp3播放器等设备的基本组件，它们渗透到我们的许多商务和休闲活动中，因此具有巨大的商业重要性。这些设备提供了优于其他现有技术的显著优势。当这种卓越的性能与对更高记录密度和更小设备的永不满足的需求相结合时，这项技术的商业重要性在未来几年内得到了保证。每一个硬盘驱动器的核心都是高度先进的材料，即“记录介质”，这是材料科学和技术的杰作。这些材料被沉积为薄膜（ca。20 nm厚）到通常直径约6-9 cm的盘的表面上。由于记录介质是铁磁性的，所以信息可以被存储，并且磁盘的小区域（“比特”）的磁性对准由微小的微加工电磁体控制，该电磁体在磁盘以大约每分钟10000转或更高的速率旋转时扫描磁盘的表面。这些材料由尺寸非常相似的小晶粒形成，通常为8 nm，根据材料的不同，变化约为22- 30%。每个铁磁比特由大约200个这些颗粒形成。由于其明显的市场优势，有大量的文献关注这些材料的表征和性能特征。相当令人惊讶的是，对它们的磁性在晶粒本身的长度尺度上的研究相对很少。这在很大程度上是由于找到合适的物理探针，可以产生定量结果，在这些（10纳米以下）的长度尺度的问题。近年来，我们与磁存储技术领域的几家世界市场领导者（希捷、IBM、日立）合作，解决有关磁记录介质物理和磁结构的基本问题。这项工作不是常规的表征，而是试图揭示相关和通用的属性，这些属性可能对未来的媒体设计产生重要影响，特别是通过提供增强这些材料正确建模的见解。微磁建模是现代媒体行业的重要组成部分，因为它允许在日益复杂和精细的设备和材料配置中优化性能。中子提供了一种理想的方法来测量颗粒水平的磁性结构，因为它们：i）具有磁矩，允许它们散射样品中的磁性变化ii）具有波长，允许从感兴趣的长度尺度（在这种情况下为1- 30 nm）上的变化散射ii）与物质的相互作用较弱，因此不会（在这种情况下）干扰他们正在测量的系统。我们最近与市场领导者的合作利用世界领先的中子设施揭示了关于亚10 nm磁性结构的独特和重要信息，这可以极大地帮助这些材料的未来设计和建模。我们在这一领域的地位是目前世界领先的。然而，我们需要为这一方案提供更多的资源，使我们既能扩大项目，又能进行实验，确保对这项工作产生影响，因为它有潜力。这是及时的，因为我们目前可以获得最新的材料（日立），并保证获得重要的专用射束时间（PSI），以及通过响应模式射束时间应用于ISIS和ILL的进一步机会，我们有很好的记录。因此，它为一个总部设在英国的集团提供了一个机会，利用英国和欧洲的设施，在一个通常由美国研究主导的领域发挥作用。

Magnetic hard disk storage devices are found at the heart of many of the high technology system we take for granted in modern life. As essential components of devices such as computers, modern video storage devices and mp3 players, they permeate much of our business and leisure activities and are thus of enormous commercial importance. These devices offer significant advantages over other current technologies. When this pre-eminence is coupled with the insatiable demand for higher recording density and smaller devices, the commercial importance of this technology is assured for some years to come.At the heart of every hard disk drive are highly advanced materials, 'recording media', that are a tour de force of materials' science and technology. These materials are deposited as thin films (ca. 20 nm thick) onto the surface of a disk that is typically around 6-9 cm in diameter. Information may be stored since the recording media are ferromagnetic, and the magnetic alignment of small areas of the disk ('bits') is controlled by a tiny micro-machined electromagnet that scans across the surface of the disk as it rotates at a rate of around 10000 revolutions per minute or greater. The materials are formed from small grains that are remarkably similar in size, typically 8 nm with a a variation of around 22-30%, depending on the materials. Each ferromagnetic bit is formed from around 200 of these grains. Due to their obvious market pre-eminence there is a very large body of literature concerned with the characterization and performance characteristics of these materials. Rather surprisingly, there has been relatively very little investigation of their magnetic properties on the length scale of the grains themselves. This is to some large extent due to the problems of finding appropriate physical probes that can produce quantitative results at these (sub-10 nm) length scales. Over recent years we have worked in collaboration with several of the world market leaders in magnetic storage technology (Seagate, IBM, Hitachi) to address fundamental questions about the physical and magnetic structure of magnetic recording media. This work is not routine characterisation, but seeks to reveal relevant and generic properties that could have important implications for future media design, particularly by providing insight that enhances the correct modelling of these materials. Micromagnetic modelling is a vital component of the modern media industry, since it allows the optimisation of performance in increasingly complex and elaborate device and materials configurations. Neutrons provide an ideal way to measure the magnetic structure at the granular level since they:i) Have a magnetic moment that allows them to scatter off magnetic variations in the sampleii) Have a wavelength that allows scattering from variations on the length scale of interest (in this case 1- 30 nm)ii) Have a weak interaction with matter so do not (in this instance) disturb the system which they are measuring.Our recent work with market leaders makes use of world leading neutron facilities to reveal unique and important information on the sub-10 nm magnetic structure, that could greatly assist the future design and modelling of these materials. We have a position in this field that is currently world leading. However, we require more serious resourcing of this programme to allow us both to expand the project but moreover to allow us to do the experiments that will ensure the impact for this work for which it has the potential. It is timely, since we currently have in place access to the latest materials (Hitachi) and guaranteed access to significant dedicated beamtime (PSI), as well as further opportunites via responsive mode beam time application to ISIS and the ILL, for which we have an excellent record. It thus provides an opportunity for a UK based group using UK and European facilities to play a role in a field usually dominated by US researc