讲座题目：Laser-induced ultrafast demagnetization in ferromagnets: Femtomagnetism

主讲人：张国平教授

讲座时间：2015.12.23  13:30

讲座地点：中北校区理科大楼A510报告厅

报告人简介：

Guo Ping Zhang，Professor of Department of Physics Indiana State University, 99 peer-reviewed research articles published in ultrafast dynamics, nanostructures, femtomagnetism, strongly correlated electrons, interfaces and xray spectroscopy, with 11 in Physical Review Letters and 1 in Nature Physics, 3 books and 11 review chapters.

报告摘要：

Laser-induced femtosecond demagnetization (femtomagnetism) presents a new opportunity for magnetic storage technology, as it significantly shortens the read/write time, a necessity for large data storage device. However,  how a magnet can lose so much spin moment over only a few hundred femtoseconds  has been under intense debate for over adecade. In this talk, I will first review the history offemtomagnetism with emphasis on the controversy in the time-resolvedmagneto-optics. It is known that in the static magneto-optical Kerreffect (MOKE), the spin moment change  is directly correlated with the Kerr rotation angle and  ellipticity, but on a femtosecond time scale,such a correlation  becomes ill-defined. A method is presented how to overcome this problem.Then, I will discuss the all-opticalhelicity-dependent switching (AOS) in ferrimagnets. AOS potent-iallyhas its broad application  in storage devices.  Our model  predicts that an ultrafast laser pulse in general only induces a spin precession,not switching; but with appropriate parameters, the laser caneven reversespin from one direction to another. This works for both thecircularly and linearly polarized light. The spin reversal window is narrow. These unexpected results closely resemble all-opticalhelicity-dependent magnetic switching found in much more complicated ferrimagnetic rare earth compounds. Our spin-orbit coupled model may find some important applications in spin switching processes, a hot topic in femtomagnetism.