RII Track 4: Non-Reciprocal Spin-Wave Engineering in Chiral Magnets

从通信到计算，波在我们生活的许多方面都存在，是一个深入研究的课题。特别是，由于移动用户和物联网的爆炸式增长对移动数据的需求不断增加，微毫米波和毫米波在5G/毫米波无线网络等下一代技术中受到了极大的关注。然而，由于缺乏合适的材料，可重构高频器件和组件的制造一直是一个挑战。促进不对称自旋波传播的手性和磁性超材料的最新进展有望用于制造基于自旋波的微波环行器和二极管。这些自旋波是高度可配置的，因为手性磁体和不对称磁性多层中的磁相互作用可以定制，并且这些材料对外部磁场和激光脉冲高度敏感，以便进一步操纵。这种可配置、节能且多功能的微波组件的演示将为新型高频通信设备铺平道路，这些设备可用于各种应用，包括娱乐、安全和远程患者治疗。俄克拉荷马州立大学和博尔德NIST纳米级自旋动力学小组的联合努力，将加速材料发现和器件表征，以实现从几GHz到太赫兹频率工作的卓越和可重构微波组件。本研究将促进对手性磁性材料中非互易自旋波传播的基本认识，这种非互易自旋波传播是由材料中不对称交换相互作用引起的。与光波或其他波相比，这些自旋波不是微不足道的，但它们可以通过调整磁相互作用、施加外部电场和磁场或用超短脉冲激发来高度控制。磁相互作用的控制将通过磁性材料和相邻金属层的工程界面来实现，以最小化磁振子散射，但保持高度的非互易性。数值微磁模拟将用于优化器件性能和更好地理解自旋波在复杂异质结构中的传播。为此，该团队将(i)生长和合成低阻尼手性磁性材料和薄膜，（ii）精确表征其结构和磁性，以及（iii）为器件概念的发展制造微纳米级器件。宽带铁磁共振波谱、磁强计、布里渊光散射波谱、磁输运和外差磁光微波显微镜是本研究将采用的技术。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Waves are in many parts of our lives, from communication to computation, and are a subject of intense research. In particular, micro and millimeter waves have been paid great attention for next-generation technologies, e.g., 5G/millimeter-wave wireless network, due to the ever-increasing demand in mobile data by the explosion of mobile users and IoT. However, the fabrication of reconfigurable high-frequency devices and components has been a challenge due to the lack of appropriate materials. Recent developments in chiral and magnetic meta-materials that facilitate asymmetric spin-wave propagation are promising for creating microwave circulators and diodes based on spin waves. These spin waves are highly configurable because the magnetic interactions in chiral magnets and asymmetric magnetic multilayers can be tailored, and these materials are highly sensitive to external magnetic fields and laser pulses for further manipulation. The demonstration of such configurable, power-efficient, and versatile microwave components will pave the way towards new high-frequency communication devices, which can be used in various applications, including entertainment, security, and remote patient treatment.The joined effort between Oklahoma State University and Nanoscale Spin Dynamics group at NIST, Boulder, will accelerate materials discovery and device characterization for superior and reconfigurable microwave components that can operate from a few GHz up to THz frequencies. The proposed research will advance the fundamental understanding of non-reciprocal spin-wave propagation in chiral magnetic materials, which is caused by asymmetric exchange interaction in them due to the broken inversion symmetry. These spin-waves are non-trivial compared to light or other waves, but they can be highly tractable by tailoring magnetic interactions, applying external electric and magnetic fields, or exciting with ultrashort pulses. Control of magnetic interactions will be achieved by engineering interfaces of magnetic material and adjacent metal layers to minimize magnon scattering but maintain high non-reciprocity. Numerical micromagnetic simulations will be used to optimize device performance and to better understand spin-wave propagation in complex heterostructures. For this purpose, the team will (i) grow and synthesize low-damping chiral magnetic materials and thin films, (ii) precisely characterize their structural and magnetic properties, and (iii) fabricate micro and nanoscale devices for the development of device concepts. Broadband ferromagnetic resonance spectroscopy, magnetometry, Brillouin light scattering spectroscopy, magnetotransport, and heterodyne magneto-optical microwave microscopy are the techniques to be employed in this investigation.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.