Collaborative Research: Spin Torque Oscillators Based on Electric and Thermal Spin Currents in Self Assembled Ferromagnetic Nanowire Arrays

该项目旨在利用自组装铁磁纳米线的有序阵列，研究由电和热自旋电流驱动的自旋传递扭矩，并研究这些紧密排列的自旋扭矩振荡器阵列中的非线性磁化动力学。这项合作研究的目标是：(i)研究由铁磁纳米线产生的电和热自旋力矩对电势和温度梯度的响应；（ii）研究强耦合自旋传递转矩振荡器二维六角形排列中的非线性集体磁化动力学；（三）基于锁相自旋转矩振荡器阵列研制高功率微波压控振荡器。所提出的自旋转矩振荡器阵列由电沉积在阳极氧化铝模板上的六边形有序钴纳米线组成。这些纳米线将作为自旋电流注入器，注入到所有注入器共同使用的薄铁磁薄膜中。自旋电流将由施加在纳米线上的电压或热梯度产生。在共铁磁层中传播的自旋波将促进各个自旋转矩振荡器之间的耦合。超快磁动力学电检测、宽带铁磁共振和磁力显微镜将用于表征自旋转矩振荡器阵列中的非线性磁化动力学。该研究将促进对由电流和自旋电流驱动的大振幅磁化动力学的理解，这对于开发下一代超快和非易失性磁电子器件（如硬盘读取头和无线通信系统）具有重要意义。该研究计划还将对同一系统中热驱动自旋电流与更常见的自旋极化电流的相对强度进行基准测试。本研究开发的微波压控振荡器将对信息存储和电信行业产生重大的技术影响。在研究人员的指导下，博士生、本科生和高中生将参与该项目。该项目提供的纳米制造和独特测量技术的实践培训将为美国磁电子工业的专家做好准备，该工业目前正经历从微尺度到纳米尺度的快速过渡。这些项目将继续吸引来自少数族裔服务机构（如加州州立大学）的代表性不足的学生，以及当地K-12学生参与研究项目。在教育课程中，所有研究人员都开发了纳米科学和纳米技术课程，并为研究生和本科生提供了一系列演示。该项目由电气、通信和网络系统部（ECCS）的电子、光子学和磁性器件计划（EPMD）和材料研究部（DMR）的电子和光子材料计划（EPM）共同资助。

Intellectual merit of the proposed activity: The project aims to study spin transfer torques driven by electric and thermal spin currents by utilizing ordered arrays of self-assembled ferromagnetic nanowires, and to investigate the nonlinear magnetization dynamics in these closely packed spin torque oscillator arrays. The objectives of this collaborative research are: (i)to study electric and thermal spin torques generated by a ferromagnetic nanowire in response to electric potential and temperature gradients; (ii) to study nonlinear collective magnetization dynamics in the hexagonally packed two dimensional arrays of strongly coupled spin transfer torque oscillators; and(iii)to develop a high-power microwave voltage controlled oscillator based on an array of phase locked spin torque oscillators.The proposed array of spin torque oscillators consist of hexagonally ordered cobalt nanowires electrodeposited in anodized alumina template. These nanowires will serve as spin current injectors into a thin ferromagnetic film common to all injectors. Spin currents will be generated by either voltages or thermal gradients applied across the nanowires. Coupling among the individual spin torque oscillators will be facilitated by spin waves propagating in the common ferromagnetic layer. Ultrafast electrical detection of magneto-dynamics, broadband ferromagnetic resonance and magnetic force microscopy will be used to characterize the nonlinear magnetization dynamics in the array of spin torque oscillators. The proposed research will advance the understanding of the large-amplitude magnetization dynamics driven by electric and spin currents, which is important for the development of the next generation ultrafast and non-volatile magneto-electronic devices such as hard drive read heads and wireless communication systems. This research program will also benchmark the relative strength of thermally driven spin currents against the more common spin-polarized electric currents in the same system.Broader impact of the proposed activity: The microwave voltage controlled oscillator developed in this research will have a significant technological impact on information storage and telecommunication industries. PhD students, as well as undergraduates and high school students will take part in this program under the guidance of the investigators. The practical training in nanofabrication and unique measurement techniques offered by this program will prepare specialists for the USA magneto-electronics industry that are currently undergoing a rapid transition from micro- to nano-scale. The PIs will continue to attract underrepresented students from minority-serving institutions, such as California State Universities, as well as local K-12 students to participate in the research projects. In the education curriculum, all investigators have developed courses on nanoscience and nanotechnology with a series of demonstrations for graduate and undergraduate students.This project is jointly funded by the Electronics, Photonics, and Magnetic Devices Program (EPMD) in the Division of Electrical, Communications and Cyber Systems (ECCS) and by the Electronic and Photonic Materials Program (EPM) in the Division of Materials Research (DMR).