垂直易磁化的半金属性磁矩补偿型人工结构的设计、制备与磁动力学特性研究

Spintronic devices with high frequency and high speed have important potential applications in high density magnetic recording, millimeter wave communication and magnetic random access memory. Several strict demands on the magnetic material are needed to satisfy simultaneously: high magneto-crystalline anisotropy, high spin polarization, low saturation magnetization and low magnetic damping factor. Half-metallic full compensated ferrimagnet (HM-FCF) not only behaves magnetically like an antiferromagnet, but also has a high spin polarization and low magnetic damping factor, which make it an ideal candidate for this kind of spintronic devices. In this project, artificial superlattice structures composed of Mn-based ordered alloys with perpendicular magnetic anisotropy and low magnetic damping factors and Co based half metals with high spin polarization are used to break through the preparation problem of HM-FCF materials with high perpendicular anisotropy. Magnetization dynamic behaviors of the film will be studied by a time-resolved magneto-optical Kerr system. Furthermore, nanoscale devices will be fabricated, and the dependence of magnetization dynamic behaviors in them such as the precession and switching process on the interfacial coupling strength and degree of compensation will be studied by the steady and dynamic electrical measurements. New artificial materials for electrically induced ultrafast magnetization precession and switching will be explored, which will provide support for the next generation spintronic devices with high frequency and high speed.

高频、高速自旋电子器件在高密度磁记录、毫米波通讯、磁随机存储器等方面具有潜在的应用价值。这对磁性材料提出了苛刻的要求，需要同时具有高磁晶各向异性、高自旋极化度、低饱和磁化强度以及低磁阻尼因子等特性。半金属性磁矩完全补偿型亚铁磁性材料（half-metallic full compensated ferrimagnet, HM-FCF）不仅具有类似反铁磁材料的磁性行为特点，同时还具有高自旋极化度以及低磁阻尼因子的优点，是研发高频、高速自旋电子器件的理想载体。本项目借助分子束外延技术，将高垂直磁各向异性、低磁阻尼因子的Mn基有序合金与高自旋极化度的Co基半金属结合，通过构建反铁磁直接耦合的人工超晶格结构，突破高垂直各向异性HM-FCF材料的制备难题，并采用时间分辨磁光克尔测试技术研究宏观超晶格薄膜中的超快磁动力学特性，结合稳态、动态电学测量技术进一步研究其纳米器件中磁矩的超快进动及翻转等特性。

Co基Heusler合金通常具有远高于室温的居里温度、高自旋极化率、低磁阻尼因子，且与GaAs、MgO等衬底均具有良好的晶格匹配度。基于Co基Heusler合金的人工合成反铁磁体具有杂散磁场减小和磁稳定性增强等优点，其其层间交换耦合作用强度可调，更容易被外界操控和检测，可以应用在超快磁随机存储器和高频振荡器等器件中，受到广泛的关注。本项目通过分子束外延设备优化制备高质量的垂直磁各向异性MnAl、Co2MnSi、Co2MnAl及其异质结人工结构，通过XRD、SQUID、PPMS 等常规手段研究其宏观稳态磁学特性；在此基础上，采用时间分辨磁光克尔系统测试研究薄膜的磁动力学特性，再通过微纳加工技术制备纳米尺寸器件，并采用时间域全电学测试手段探测其纳米结构中的磁动力学特性。通过本项目的执行，实现了电流驱动其自旋轨道矩磁化翻转，临界电流密度约为5×10^7A/cm2；制备出L10-MnAl/MgO/Co2MnSi/MnAl垂直磁性隧道结，标定出其隧穿磁阻率的温度依赖关系；通过磁、电输运揭示了Co2MnGa 薄膜中费米能级附近可能存在的能带交叉。