Nonreciprocal sound for spin wave dynamics

表面声波（SAW）已经进入许多日常设备，如射频滤波器和传感器，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减少。相干SAW在MHz到GHz的范围内可以有效地发射和检测压电基板上的周期性金属光栅。然而，SAW通常传播噪声。正如我们最近所证明的，共振磁声耦合的互易SAW与非互易自旋波（SW）引起的压电/铁磁混合系统中的非互易磁声波传输，这打开了可能性，建立新型的非互易微波器件。基于这些第一个结果，这个联合项目的目的是探索这些非互易性的影响，在新的材料systems.First，我们建议研究的非互易性的GHz频率磁声波的混合器件结合压电基板与薄膜合成反铁磁体和补偿亚铁磁体。因此，我们将研究SAW和SW模式的相对手性对非互易性的影响，并利用内部磁声驱动场可以耦合到净磁矩消失的材料的SAW-SW耦合。这些定制的压电/磁性混合物可以用作小型化的，片上的，非互易微波元件，如隔离器的基础。其次，我们建议使用SAW的SW光谱。为此，我们将利用磁声相互作用来表征SW分散体和磁性薄膜中的磁织构与界面Dzyaloshinskiii-Moriya相互作用。由于SAW的波长可以短于光波长，我们希望我们的方法允许高灵敏度光谱超出传统磁光技术的分辨率限制。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换。通过这些空间和相位分辨技术，我们可以确定SAW和SW的波矢量，从而详细地解决SAW对SW的激发（反之亦然）。这将使我们能够验证和完善我们的模型假设的磁振子声子相互作用。

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.