Advanced Characterisation of Magnetic Recording Media using Neutron Scattering

在现代生活中，许多我们认为理所当然的高科技系统的核心都有磁性硬盘存储设备。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，它们渗透到我们的大部分商业和休闲活动中，因此具有巨大的商业重要性。与其他当前技术相比，这些设备提供了显著的优势。当这种卓越的优势与对更高记录密度和更小设备的永无止境的需求相结合时，这项技术的商业重要性在未来几年肯定是肯定的。每个硬盘驱动器的核心都是高度先进的材料-记录介质，这是材料科学和技术的巡回演出。这些材料以薄膜(约20纳米厚)的形式沉积在通常直径约为6-9厘米的磁盘表面上。因为记录介质是铁磁性的，所以可以存储信息，并且盘的小区域(位)的磁对准由微小的微机械加工的电磁铁控制，当盘以大约每分钟10000转或更大的速度旋转时，该电磁铁在盘的表面上扫描。这些材料是由大小非常相似的小颗粒组成的，通常是8纳米，根据材料的不同，变化约为22%-30%。每个铁磁性比特由大约200个这样的颗粒组成。由于它们明显的市场优势，有大量的文献关注这些材料的表征和性能特征。令人惊讶的是，在颗粒本身的长度尺度上，对它们的磁性的研究相对很少。这在很大程度上是由于寻找合适的物理探针的问题，这些物理探针可以在这些(亚10 nm)长度尺度上产生定量结果。近年来，我们与几家磁存储技术领域的世界市场领先者(希捷、IBM、日立)合作，解决有关磁记录介质的物理和磁结构的基本问题。这项工作不是常规的定性，而是试图揭示可能对未来媒体设计产生重要影响的相关和一般性属性，特别是通过提供洞察力来加强这些材料的正确建模。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。中子提供了一种在颗粒级测量磁性结构的理想方法，因为它们：i)具有磁矩，使它们能够散射样品中的磁性变化；i)具有波长，允许从感兴趣的长度范围(在此情况下为1-30 nm)的变化中进行散射；ii)与物质具有弱相互作用，因此不(在此情况下)干扰它们所测量的系统。我们最近与市场领先者的合作利用世界领先的中子设施来揭示关于亚10 nm磁性结构的独特而重要的信息，这将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目前处于世界领先地位。然而，我们需要为这一方案提供更多的资源，以便我们既能扩大该项目，又能让我们进行实验，以确保对这项有潜力的工作产生影响。这是及时的，因为我们目前已经获得了最新的材料(日立)，并保证获得重要的专用波束时间(PSI)，以及通过响应模式波束时间应用于ISIS和ILL的更多机会，我们在这方面有很好的记录。因此，它为使用英国和欧洲设施的英国集团提供了在通常由美国研究主导的领域发挥作用的机会

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