Modeling of Ultrafast Magnetization Dynamics at High temperatures

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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.