Experimental investigation of topological excitations in magnetic tunneling junctions

非技术摘要：近年来，人们发现隐藏在某些材料中的性质可以被电或磁激发，以设计下一代电子产品。Skyrmion是一种纳米尺度的旋转磁性图案，是磁性材料中这种拓扑激发的一个例子。磁隧道结可以说是近年来发展起来的最有前途的自旋电子学设备，用于数据存储、传感和逻辑计算。通常，在这种应用中，在磁性隧道结中使用两个相反的铁磁性状态来存储二进制数据。这项实验研究开发了新的方法来创建、探测和操纵磁隧道结中的磁性天米子态。基于Skyrmion的磁性隧道结预计将消耗更少的能源，以更高的速度运行，并对材料无序更加坚固，为重大技术进步提供平台。该项目为研究生准备在自旋电子学和微波电子学这两个对我们的社会具有重要经济意义的技术领域进行熟练的研究，这些领域训练有素的物理学家的需求量很大。纳米磁学和自旋电子学研究生课程的开发有效地将所提出的研究整合到教学主题中，以满足来自物理、电气工程、材料科学和化学等多学科领域的学生的需求。技术摘要：本研究的目的是研究磁隧道结中单个和相互作用的磁天子。电流驱动的自旋转移力矩、电压控制的磁各向异性和外加磁场矢量被用作控制海森堡交换相互作用和Dzyaloshinskii-Moriya相互作用之间的相互作用的手段。实验绘制了竞争磁激发的相图。亚纳秒的电压脉冲被用来确定地产生和湮灭单个的天空微子。发展了一种共振光谱技术，利用Skyrmion的呼吸模式来进行表征，包括能量色散、核心尺寸等。研究了较大器件中的Skyrmions相互作用，如Skyrmion晶体。这项裁决反映了NSF的法定使命，通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

Nontechnical Abstract: In recent years, it has been discovered that properties hidden inside certain materials can be excited electrically or magnetically, to design the next generation of electronics. Skyrmion, a nanoscale whirling magnetic pattern, is an example of such topological excitations in magnetic materials. The magnetic tunnel junction is arguably the most promising spintronics device, developed in the recent years, for data storage, sensing, and logic computation. Generally, in such applications two opposite ferromagnetic states are used to store binary data in the magnetic tunneling junctions. This experimental research develops new ways to create, probe, and manipulate the magnetic skyrmion states in the magnetic tunnel junctions. The skyrmion-based magnetic tunnel junctions are expected to consume less energy, operate at a higher speed, and be more robust against material disorder, providing a platform for significant technological advances. The project prepares graduate students for skilled research in both spintronics and microwave electronics, technical areas that are of great economic importance to our society, and well-trained physicists in these areas are in high demand. The development of a graduate level course on nano-magnetics and spintronics effectively integrates the proposed research into a teaching topic in demand, to fulfill the needs of students from multidisciplinary areas such as Physics, Electrical Engineering, Material Sciences, and Chemistry.Technical Abstract: The objective of this research is to study individual and interacting magnetic skyrmions in magnetic tunnel junctions. Current-driven spin-transfer torque, voltage controlled magnetic anisotropy, and applied magnetic field vector are used as a means to control the interplay between the Heisenberg exchange interaction, responsible for ferromagnetism, and the Dzyaloshinskii-Moriya interaction, which gives rise to stable skyrmions. A phase diagram for competing magnetic excitations is mapped out experimentally. Sub-nanosecond electrical voltage pulses are used to deterministically create and annihilate individual skyrmions. A resonant spectroscopy technique is developed to use the breathing mode of skyrmions to carry out characterizations, including energy dispersion, core size, etc. Interacting skyrmions in larger devices, as in the case of a skyrmion crystal, are studied. The implications of disorder, particularly for edge imperfection, are investigated.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.