基于圆偏振红外和太赫兹脉冲双泵浦的自旋非热双光磁调控研究

The use of ultra-short pulse non-thermal optical-magneto manipulation can study the dynamics of electron spin of magnetic materials and can control spin in a very short period of time, which is very important for the development of modern information technology. There are two typical types of non-thermal spin optical-magneto manipulation: one is the use of circularly polarized light to induce a magnetic field by Inverse Faraday Effect; the other is to use spin-related resonance mode of the terahertz pulse to excite the magnetic material. Spin control can be achieved by either of these two types. However, their interrelations, similarities and differences, and the dual- manipulation mechanisms and the spin dynamics under the joint control are not yet known. This project aims at this key scientific problem in the field of ultrafast optical-magneto manipulation, and will design and build up a strong magnetic field (10 T), variable temperature (8-350 K), variable wavelength (240-2600 nm, 0.1-2 THz) ultrafast dual pumping optical-magneto manipulation system based on the existing single system. The spin-dynamics study of magnetic materials such as antiferromagnetic LaFeO3 and ferromagnetic SmFeO3 was carried out using circularly polarized infrared and terahertz pulsed dual pumping methods in this system; the similarities and differences of the dual-pumping optical-magneto manipulation were explored. The ultrafast magnetic properties and mechanisms under dual manipulation are expected to observe a richer magnetic excitation and spin oscillation process, which lay the foundation in the field of ultrafast magnetic storage, spintronics and so on.

利用超短脉冲进行非热光磁调控、研究磁性材料电子自旋动力学和在极短时间内实现自旋操控，对现代信息技术有重要意义。实现自旋非热光磁调控有两种典型方式：一是用圆偏振光通过逆法拉第效应诱导磁场；二是用太赫兹脉冲激发磁性材料的自旋相关共振模式。这两种方式都可实现自旋调控，但他们之间的相互关系和异同，以及共同作用下双调控机制和自旋动力学尚不清楚。本项目针对这一超快光磁调控中的关键科学问题，拟在现有分立系统的基础上，设计/组建一套强磁场(10T)、变温(8-350K)、变波长(240-2600nm、0.1-2THz)的超快双泵浦光磁调控系统。通过该系统的圆偏振红外和太赫兹脉冲双泵浦方法对反铁磁LaFeO3和铁磁SmFeO3等磁性材料进行自旋动力学研究；理清双泵浦光磁调控的相同点和差异，探索双调控下的超快磁特性与机制；有望观测到更丰富的磁激发和自旋振荡过程，为超快磁存储、自旋电子学等领域的研究奠定基础。

在更短的时间和更小的空间尺度上实现电子自旋的调控对自旋电子学、现代信息存储技术的发展具有重要意义，本项目开展了磁性和氧化物薄膜材料的超快动力学和超快光磁调控研究。设计和组建了强磁场下的超快光磁调控系统，可以实现温度（2-300K）、磁场（-7T到7T）、波长（800nm和400nm，也可引入OPA）和偏振（圆偏振光和线偏振光）等外部参量的变化。具备磁性LOOP测量、超快反射率/透过率、TR-MOKE（超快退磁、自旋进动）和逆法拉第效应等测试功能。开展了太赫兹波段的光磁调控系统建设，获取了强太赫兹光源。利用超快光磁调控系统，获取了超快泵浦-探测的信号，主要研究了Cr2Ge2Te6等样品的超快磁动力学和LaRhO3等样品的超快声子动力学过程。发现了二维范德瓦尔斯半导体磁性材料Cr2Ge2Te6中超长自旋弛豫现象，并对比研究了二维范德瓦尔斯金属材料Fe3GeTe2和三维金属Cr3Te4材料的超快自旋动力学过程。观测到了CoFe/SmIG/GGG和CoFe/GGG异质结界面的超快动力学过程，两者具有不同的进动周期，表明CoFe和SmIG之间存在界面自旋耦合。制备了各种磁性和氧化物薄膜材料，如LaRhO3和Y2NiMnO6等。观测到了LaRhO3的光电导现象和Cr5Te8微观磁畴等现象。开展了HoFeO3和HoYFeO3反铁磁材料的单晶自旋重取向的掺杂效应与磁控效应的太赫兹光谱研究。观测到了LaRhO3/SrTiO3和Y2NiMnO6/SrTiO3等薄膜中的超快声子行为，超快声子的振荡周期、频率和泵浦功率、波长和外加磁场无关，和探测光的入射角度、波长等有关。并利用双泵浦的方法，实现了超快声子的干涉相长、干涉相消的相干调控研究。本项目的进展为下一步的自旋电子学、超快磁动力学和超快声子动力学的科学研究及其调控工作提供了研究经验。