SUB-PICOSECOND CONTROL OF NANO-MAGNETS

现代膝上型计算机的数据存储容量和运行速度比占据几个大房间的第一代计算机大几个数量级。为了保持进度，必须进一步减少物理位大小和数据访问时间。在这种情况下，纳米磁性技术正在成为数十亿美元的高速微型数据存储和处理设备市场上最强大的参与者之一。这构成了拟议研究计划的主要实际动机，该计划的总体目标是通过亚皮秒的光和磁脉冲获得对纳米级磁性结构的更快控制。这将需要解决几个根本的重要问题，将我们对超快纳米尺度磁动力学的知识和理解扩展到一个新的水平。该项目利用的基本现象是逆法拉第效应，由于这种逆法拉第效应，圆偏振光脉冲可以产生亚皮秒的磁场脉冲(所谓的光磁场)，比电子或超快光电二极管产生的最快的电脉冲和磁脉冲短几个数量级。来自超快激光的光脉冲产生的脉冲光磁场将被用来操纵磁化，要么直接使用光磁场本身，要么通过在一种名为法拉第光学变压器的新型设备中将其转换为Oersted磁场脉冲来间接操作。在磁性薄膜和纳米级元件中激发的磁化进动将通过测量延迟的光脉冲(探头)从泵浦的样品反射时获得的偏振变化来磁光跟踪。磁化动力学将在小幅度(自旋波)和大幅度(180度反转)两种情况下进行研究和成像。将研究多脉冲光磁场、Oersted场和/或微波场的组合作用，并用于优化磁开关特性。拟议的研究属于EPSRC的纳米世界(磁性材料)、量子领域(光与物质的相互作用)和微型机(光子学和光电子学)优先领域。

The data storage capacity and the speed of operation of a modern laptop computer are orders of magnitude greater than those of the first computers that occupied several large rooms. To maintain the pace of progress, both the physical bit size and the data access time must be reduced even further. Under these circumstances, the nano-magnetic technology is becoming one of the strongest players in the multibillion dollar market for high speed miniature devices for data storage and processing.This constitutes the main practical motivation for the proposed research programme which has the overall aim of gaining an ever-faster control of nanoscale magnetic structures by means of sub-picosecond optical and magnetic pulses. This will require that several issues of fundamental importance be resolved, extending our knowledge and understanding of ultrafast nano-scale magnetic dynamics to a new level.The basic phenomenon exploited in the project is the Inverse Faraday Effect due to which circularly polarised optical pulses can generate sub-picosecond pulses of magnetic field (so called photo-magnetic field), which are orders of magnitude shorter than the fastest electrical and magnetic pulses produced electronically or in ultrafast photo-diodes. The pulsed photo-magnetic field due to optical pulses from an ultrafast laser will be used to manipulate the magnetisation either directly, by using the photo-magnetic field itself, or indirectly, by converting it into pulses of the Oersted magnetic field within a novel device called a Faraday Optical Transformer. The magnetisation precession excited in magnetic thin films and nanoscale elements will be then traced magneto-optically by measuring the change of polarisation acquired by a delayed optical pulse (a probe ) upon reflection from the pumped sample. The magnetisation dynamics will be studied and imaged in both small (spin waves) and large (180 degrees reversal) amplitude regimes. A combined action of multiple pulses of photo-magnetic, Oersted and / or microwave fields will be investigated and used to optimize magnetic switching characteristics.The proposed research falls within the EPSRC's Nano World (Magnetic materials), Quantum Realm (Interaction of Light and Matter), and Miniature Machines (Photonics and Optoelectronics) priority areas.