EFRI NewLAW: Non-Reciprocal Magneto-Acoustic Waves in Chiral Magnetic Systems

波通常用于通信和成像。例子包括使手机能够工作的微波和使超声成像成为可能的声波。通常情况下，这些波可以从源头向任何方向自由传播。如果使这种波只向一个特定方向传播，那么这种波的许多实际应用将得到改进。例如，这种单向波使通信设备可以使用同一天线同时发送和接收信号。这被称为全双工通信。该项目的一个目标是创造新的磁性材料，在这种材料中，微波和超声波只向一个方向传播。另一个目标是制造一种新型的非常紧凑的片上微波和声学设备，称为循环器，基于这些新材料。这种循环器是使全双工通信成为可能的核心要素。在这个项目的过程中，主要研究人员将培训一些本科生和研究生，包括那些来自传统黑人学院和大学的学生，在现代材料工程、纳米制造和微波测量技术方面，这将增强美国的科学和工程劳动力。该项目有两个主要目标：(i)开发支持强非互反自旋波和磁声波的手性材料和超材料；（ii）展示基于非互反波的声信号循环器和可重构微波循环器。将采用两种产生非互易波的方法。在第一种方法中，磁性薄膜中的波非互易性将通过与重元素掺杂界面的反对称交换相互作用或通过施加垂直于薄膜表面的电场通过自旋挠曲电相互作用诱导。在第二种方法中，缺乏反演对称性的新型磁性超材料将由铁磁性纳米元件阵列制成。在这些超材料中，可以激发几种类型的非互易自旋波，包括频谱保护模式和拓扑保护边缘态。通过采用具有强共振磁弹性耦合的材料，将自旋波的非互易性转化为磁声波。根据该计划开发的非互反磁性超材料将用于制造和测试基于沿超材料边缘传播的非互反拓扑保护手性磁声波的声波循环器。制作并测试了一种基于铁磁薄膜中自旋-挠性电相互作用的可重构超紧凑微波环行器。通过外部偏置电压可以快速控制微波信号在该器件中的传播方向。该研究项目将促进我们对磁性超材料中非倒易波的理解，并将导致开发一种新型的超紧凑、片上、非倒易信号处理设备。

Waves are commonly used in communications and imaging. Examples include microwaves that enable operation of cell phones and acoustic waves that enable ultrasound imaging. Typically these waves can freely propagate in any direction away from their sources. Many practical applications of such waves could be improved if the waves were made to propagate in only one specific direction. For example, such unidirectional waves enable communication devices that can simultaneously send and receive signals using the same antenna ? this is called full duplex communications. One goal of this project is to create new magnetic materials, in which microwaves and ultrasound waves propagate in only one direction. Another goal is to make a new type of very compact on-chip microwave and acoustic devices called circulators that are based on these novel materials. Such circulators are the core elements making the full duplex communications possible. In the course of this project, the principal investigators will train a number of undergraduate and graduate students, including those from Historically Black Colleges and Universities, in modern materials engineering, nanofabrication, and microwave measurement techniques, which will enhance the U.S. science and engineering workforce.This project has two major goals: (i) development of chiral materials and meta-materials supporting strongly non-reciprocal spin waves and magneto-acoustic waves and (ii) demonstration of acoustic signal circulators and reconfigurable microwave circulators, which are based on the non-reciprocal waves. Two approaches to the generation of non-reciprocal waves will be employed. In the first approach, the wave non-reciprocity in magnetic films will be induced either via anti-symmetric exchange interactions by doping interfaces with heavy elements or via spin-flexoelectric interactions by applying an electric field perpendicular to the film surface. In the second approach, novel magnetic metamaterials lacking inversion symmetry will be made from arrays of ferromagnetic nano-elements. In these meta-materials, several types of non-reciprocal spin waves can be excited including spectrally protected modes and topologically protected edge states. By employing materials with strong resonant magneto-elastic coupling, the spin-wave non-reciprocity is transferred to magneto-acoustic waves. Non-reciprocal magnetic meta-materials developed under this program will be used to make and test acoustic wave circulators based on non-reciprocal, topologically protected chiral magneto-acoustic waves propagating along the meta-material edges. A reconfigurable ultra-compact microwave circulator based on spin-flexoelectric interactions in ferrimagnetic thin films will be made and tested. The direction of microwave signal propagation in this device can be rapidly controlled via external bias voltage. This research project will advance our understanding of non-reciprocal waves in magnetic meta-materials and will result in the development of a new class of ultra-compact, on-chip, non-reciprocal signal processing devices.