Modeling of Ultrafast Magnetization Dynamics at High temperatures

高温下超快磁化动力学建模

• 批准号: 1404542
• 负责人: Shufeng Zhang
• 金额: $ 30万
• 依托单位: University of Arizona
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-08-15 至 2018-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1404542&HistoricalAwards=false
• 关键词: Modeling; Ultrafast; Magnetization; Dynamics; temperatures

Technological advances today for smaller and faster information storage devices such as hard disk drives and magnetic random access memory have encountered unavoidable challenges due to fundamental limitations placed on the current read/write schemes. One of the most exciting ideas to meet this challenge is to utilize an ultrafast laser or an ultra-short pulsed electric current to manipulate magnetic states. Indeed, it has been experimentally discovered that it is possible to control the magnetic states in less than one picosecond (ps) by these methods. Inevitably, one enters a new area of science and technology involving ultrafast dynamics at high temperatures, as oppose to the present-day magnetic technology which is 1000 times slower (nanoseconds) at room temperatures. In this research proposal, one focuses on the detailed understanding of the physical processes, determines key factors that control the magnetic states and develops quantitative modeling tools which can simulate magnetization dynamics with desired accuracy. It is anticipated that the research outcome can be broadly applied to explain and predict novel magnetization dynamic phenomena observed experimentally, and more importantly, to provide essential computational tools for application of future magnetic technologies based on ultrafast and high temperature magnetization dynamics such as heat-assisted magnetic recording technology. The other proposed activities include strong collaboration with industry previously established, training of graduate students via extensive mentoring and industry laboratories visiting. A new spintronics course with the emphasis on the recent progresses in spintronics physics and devices has been initiated and will be taught in the Fall semester of 2014.This scientific program aims at developing an effective equation that can be broadly used for quantitatively modeling of magnetization dynamics at a wide range of temperatures and at ultrafast time scales. At present, the reliable and powerful simulation tool for room-temperature nanosecond magnetization dynamics is based on the Landau-Lifshitz (LL) equation, which is deemed to fail at the temperature close or above the Curie temperature. What is needed, from the view point of theory and simulation, is a better simulation tool to replace the LL equation so that the magnetization dynamics at high temperature and at ultrafast timescales can be quantitatively addressed. Built on the preliminary study of the microscopic origins of fast relaxations, the quantum kinetic approach will be used to establish a self-consistent dynamic equation. After the proposed dynamic equation for the magnetization vector is validated, extensive numerical simulations will be carried out for the element-specific dynamics in magnetic multilayers and alloys. Two particular device-relevant dynamics processes, laser induced demagnetization and heat-assisted magnetic writing, will be extensively studied and optimized.

由于对当前读/写方案的基本限制，当今用于更小和更快的信息存储设备（诸如硬盘驱动器和磁性随机存取存储器）的技术进步遇到了不可避免的挑战。迎接这一挑战的最令人兴奋的想法之一是利用超快激光或超短脉冲电流来操纵磁状态。实际上，已经通过实验发现，通过这些方法可以在小于一皮秒（ps）内控制磁状态。不可避免地，人们进入了一个新的科学和技术领域，涉及高温下的超快动力学，而现在的磁技术在室温下慢1000倍（纳秒）。在这项研究中，一个重点是详细了解的物理过程，确定控制磁状态的关键因素，并开发定量建模工具，可以模拟磁化动态与所需的精度。预计研究成果可广泛应用于解释和预测实验观察到的新型磁化动力学现象，更重要的是，为基于超快和高温磁化动力学的未来磁技术（如热辅助磁记录技术）的应用提供必要的计算工具。其他拟议的活动包括与以前建立的行业密切合作，通过广泛的指导和行业实验室访问培训研究生。 2014年秋季学期开设了一门新的自旋电子学课程，重点介绍自旋电子学物理和器件的最新进展。该课程旨在建立一个有效的方程，可广泛用于在宽温度范围和超快时间尺度下定量建模磁化动力学。目前，用于室温纳秒磁化动力学的可靠且强大的模拟工具是基于Landau-Lifshitz（LL）方程，该方程被认为在接近或高于居里温度的温度下失效。从理论和模拟的角度来看，需要一个更好的模拟工具来取代LL方程，以便可以定量地解决高温和超快时间尺度下的磁化动力学。在对快弛豫的微观起源进行初步研究的基础上，利用量子动力学方法建立了自洽的动力学方程。在验证了所提出的磁化矢量的动力学方程之后，将对磁性多层膜和合金中的特定元素动力学进行广泛的数值模拟。两个特殊的设备相关的动力学过程，激光诱导退磁和热辅助磁写入，将被广泛研究和优化。