Nonreciprocal sound for spin wave dynamics

表面声波(SAW)已经进入了许多日常设备，如射频过滤器和传感器，这要归功于SAW的波长与相同频率的自由空间微波相比大大降低。在带有周期性金属栅压电衬底上，可以有效地发射和检测MHz到GHz范围内的相干声表面波。然而，锯子通常是相互传播的。正如我们最近所证明的那样，互易锯片与非互易自旋波的共振磁声耦合导致了非互易磁声波在压电/铁磁混合系统中的传输，这为构建新型的非互易微波器件提供了可能。基于这些第一个结果，本联合项目旨在更详细地探索新材料系统中的这些非互易效应。首先，我们建议研究将压电衬底与薄膜合成反铁磁体和补偿亚铁磁体相结合的混合器件中GHz频率磁声波的非互易性。因此，我们将研究声表面波和波的相对手征性对非互易性的影响，并利用内部磁声驱动场与净磁矩为零的材料耦合来实现声表面波与波的耦合。这些量身定做的压电式/磁性混合体可用作小型化、片上、非互易微波元件的基础，例如隔离器。其次，我们建议使用SAW进行短波光谱分析。为此，我们将利用磁声相互作用来表征具有界面Dzyaloshinskii-Moriya相互作用的磁性薄膜中的Sw弥散和磁性织构。由于SAW的波长可能比光学波长短，我们希望我们的方法能够实现超出传统磁光技术分辨率限制的高灵敏度光谱。最后，我们将利用磁光成像来研究相干磁振子和声子的相互作用和相互转化。有了这些空间分辨和相分辨技术，我们可以确定声表面波和慢波的波矢，从而详细地研究声表面波对慢波的激发(反之亦然)。这将使我们能够验证和改进我们对磁振子-声子相互作用的模型假设。

Surface acoustic waves (SAWs) have made their way into many everyday devices, such as rf-filters and sensors, thanks to the greatly reduced wavelength of SAWs compared to free-space microwaves of the same frequency. Coherent SAWs in the MHz- to GHz-range can be efficiently launched and detected on piezoelectric substrates with periodic metallic gratings. However, SAWs are in general propagating reciprocally. As we have recently demonstrated, resonant magnetoacoustic coupling of reciprocal SAWs with nonreciprocal spin waves (SWs) gives rise to nonreciprocal magnetoacoustic wave transmission in piezoelectric/ferromagnetic hybrid systems, which opens the possibility to build novel nonreciprocal microwave devices. Based on these first results, this joint project aims to explore these nonreciprocal effects in novel material systems in more detail.First, we suggest studying the nonreciprocity of GHz-frequency magnetoacoustic waves in hybrid devices combining piezoelectric substrates with thin film synthetic antiferromagnets and compensated ferrimagnets. Thereby, we will investigate the impact of relative chirality of SAW and SW modes on nonreciprocity and exploit the SAW-SW coupling by internal magnetoacoustic driving fields that can couple to materials with vanishing net magnetic moment. These tailored piezoelectric/magnetic hybrids can be used as a basis for miniaturized, on-chip, nonreciprocal microwave elements, such as isolators. Second, we suggest using SAWs for SW-spectroscopy. To this end, we will exploit magnetoacoustic interactions to characterize SW dispersions and magnetic texture in magnetic thin films with interfacial Dzyaloshinskii-Moriya interaction. Because the wavelength of SAWs can be shorter than optical wavelengths, we expect that our method allows for highly sensitive spectroscopy beyond the resolution limits of conventional magneto-optical techniques. Finally, we will use magneto-optic imaging to study the interaction and interconversion of coherent magnons and phonons. With these spatially- and phase-resolved techniques, we can determine wave vectors of SAWs and SWs and thus address the excitation of SWs by SAWs (and vice versa) in detail. This will allow us to verify and refine our model assumptions for magnon-phonon interactions.