Fundamental aspects of all-optical single pulse switching in nanometer-sized magnetic storage media

数字存储的数据量越来越大，需要新的技术概念来实现更高的密度和更快的向存储介质的写入速度。经过40多年的小型化，传统的磁数据存储技术正面临着它们的极限。从本质上讲，在磁性硬盘上存储信息就是设置最小磁域的磁化强度，从而创建位。传统上，这是通过直接在磁盘表面上方飞行的小电磁铁感应磁场来实现的。随着使用这种方法的优化可能性在技术上接近尾声，新的方法变得有趣起来。全光螺旋度相关磁化切换(AO-HDS)有可能进一步缩小比特，同时加快写入过程。我们以前对颗粒状FePT硬盘介质的研究表明，由逆法拉第效应(IFE)触发的随机开关是圆偏振激光脉冲确定性开关机制的主要来源，我们将克服这一点。我提出了一个研究项目，利用圆偏振的飞秒激光脉冲在近红外到中红外的波长范围内进行AO-HDS开关实验。在这项研究中，将阐明粒子介质中不同光子能量的IFE的效率，以及IFE与磁性圆二向色性之间的相互作用。利用我在时间分辨磁光克尔效应(TR-MOKE)测量方面的专业知识，可以同时实施这些实验，以进一步分析飞秒到皮秒时间尺度上的磁化和开关动力学。为了研究等离子体和介电近场放大和开关增强，将在磁盘介质的界面上开发所需的纳米结构。与实验小组的两项合作将扩展对开关实验的分析，使用克尔显微镜来成像开关后的磁性结构，并使用磁力显微镜来研究AO-HDS的微观机制和起源。该项目被嵌入到现有的成功的理论合作中，其中将扩展为热自旋建模、从头算IFE计算和热宏观自旋建模开发的现有工具，以增强其描述性光谱。

Increasing amounts of data for digital storage, call for new technological concepts enabling higher densities with faster writing speeds to the storage media. After over 40 years of miniaturization, conventional techniques for magnetic data storage are facing their limits. Essentially, storing information on a magnetic hard disk is setting the magnetization of smallest domains and thus creating bits. Conventionally, this is done by small electromagnets flying directly above the disk’s surface inducing a magnetic field. As the optimization possibilities using this method are technologically reaching an end, new approaches become interesting. All-optical helicity-dependent magnetization switching (AO-HDS) has the potential for further bit shrinking and at the same time to speed up the writing process. Our precedent studies with granular FePt hard disk media point to stochastic switching triggered by the Inverse Faraday Effect (IFE) as the major source of the deterministic switching mechanism with circularly polarized laser pulses, which we will overcome. I propose a research project performing AO-HDS switching experiment using circularly polarized femtosecond laser pulses in the wavelength range from near-infrared to midinfrared. In this study, the efficiency of the IFE with respect to different photon energies in granular media together with the interplay between the IFE and the magnetic circular dichroism will be elucidated. Using my expertise in time-resolved magneto-optical Kerr-effect (TR-MOKE) measurements will allow implementing these experiments alongside to further analyze the magnetization and switching dynamics on femto- to picosecond time scales. For the examination of plasmonic and dielectric near field amplification and switching enhancement, the required nanostructures at the interface to the disk media will be developed. Two collaborations with experimental groups will extend the analysis of the switching experiments by employing Kerr-Microscopy to image the magnetic structures after switching and to study the microscopic mechanism and origin of AO-HDS using Magnetic Force Microscopy. This project is embedded into existing successful theory collaborations in which the current tools developed for thermal spin modelling, ab-initio IFE calculations and thermal macrospin modelling will be extended to enhance their descriptive spectrum.