磁滴子型自旋转矩纳米振荡器的微磁学研究

With the recent development of MRAM product, another application of the spin-transfer torque (STT) effect—spin torque oscillators (STO) has been another hot topic. The recent interest regarding on the STT has been directed towards a so-called magnetic droplet-based nano-contact STO. It has attracted a great deal of interest not only in the practical spintronic device applications but also in the field of fundamental magnetism physics. The reason for that is attributed to the special topological soliton structure of the magnetic droplet as well as the large emission power and high quality of oscillation frequency in such type of STOs. However, the microscopic understanding of the underlying mechanisms is still in its infancy. Such a frontier scientific issue will be studied in this project by using micromagnetic simulation technique. We will study the underlying physical mechanism of magnetization oscillation mode and reliability of the droplet-based STOs. The dependence of frequency characteristics on the device parameters will be clarified. Then, in order to further enhance the output power of the STOs, we will study the synchronization technique for phase locking of several to tens of magnetic droplets. We expect the proposed study through this project shall open new insights into the understanding of STT driven magnetization dynamics in droplet-based STOs and provide significant development in spintronics.

随着MRAM的产品化，自旋转矩（STT）效应的第二个重要应用——“自旋转矩振荡器（STO）”继而成为自旋电子学的又一热点课题。特别是近期发现的磁滴子（droplet）型自旋转矩振荡器引起了人们极大研究兴趣，关注领域不仅局限于自旋电子器件的应用，而且还包括基础磁性物理领域。究其原因，一方面droplet具有独特的拓扑磁孤子结构，此外它还表现出的优越频谱特性和大功率输出信号。然而，有关droplet型STO振荡器的研究目前尚处于起步阶段。本项目我们将针对这一前沿科学问题开展微磁学研究，研究droplet型振荡器的磁矩振荡模式及其稳定性问题的微观机理，揭示振荡器的频率特性与器件参数依赖关系，研究多个droplet的相位同步问题，探讨提高STT振荡器输出功率的有效方法和途径等。我们期望这些研究将有助于加深STT效应驱动的Droplet型纳米振荡器动力学特性的理解，推动相关自旋电子学的发展。

“自旋转矩纳米振荡器（STNO）”是自旋电子学领域在继MRAM之后具有产业化应用的又一热点课题，本项目我们开展了一类纳米触点（NC）型STNO详细研究。在具有垂直磁各向异性的自旋阀或磁性隧道结中，在纳米触点区域通电流可激发出磁矩的局域周期性振荡，被称为磁滴子(droplet)型自旋转矩振荡器。本项目主要取得如下研究数据和结果：（1）建立和完善了自旋转矩(STT)效应驱动的Droplet型STNO微磁学模型，研究了振荡器的激发频率与电流、电场、磁场以及器件结构参数等的依赖关系，揭示了微观机理和激发规律。（2）研究了纳米接触型STNO的振荡模式及其稳定性问题，探讨了电流和电场协同驱动下振荡模式从Droplet磁矩局域振荡模式与可传播自旋波模式的跳转行为特性。（3）研究了多个Droplet的同步问题，发展了磁耦合和微波驱动等多种同步方法；建立了电场和电流协同操控调STNO的移频键控(BFSK)方案。（4）我们还研究了磁性隧道结和人工反铁磁等纳米磁结构的铁磁共振特性，以及亚铁磁薄膜材料的界面耦合效应等。这些研究结果对低能耗、GHz频段的自旋波微波发射器件和检测器件的研发提供了可靠的技术参数和器件设计依据。共发表SCI论文18篇（含Phys. Rev. Appl.2篇，Appl. Phys. Lett. 2篇；New J. Phys. 1篇等）。