The 2024 Magnonics Roadmap.

Magnonicsis a research field that has gained an increasing interest in both the fundamental and applied sciences in recent years. This field aims to explore and functionalize collective spin excitations in magnetically ordered materials for modern information technologies, sensing applications, and advanced computational schemes. Spin waves, also known as magnons, carry spin angular momenta that allow for the transmission, storage, and processing of information without moving charges. In integrated circuits, magnons enable on-chip data processing at ultrahigh frequencies without the Joule heating, which currently limits clock frequencies in conventional data processors to a few GHz. Recent developments in the field indicate that functional magnonic building blocks for in-memory computation, neural networks, and Ising machines are within reach. At the same time, the miniaturization of magnonic circuits advances continuously as the synergy of materials science, electrical engineering, and nanotechnology allows for novel on-chip excitation and detection schemes. Such circuits can already enable magnon wavelengths of 50 nm at microwave frequencies in a 5G frequency band. Research into non-charge-based technologies is urgently needed in view of the rapid growth of machine learning and artificial intelligence applications, which consume substantial energy when implemented on conventional data processing units. In its first part, the 2024 Magnonics Roadmap provides an update on the recent developments and achievements in the field of nano-magnonics while defining its future avenues and challenges. In its second part, the Roadmap addresses the rapidly growing research endeavors on hybrid structures and magnonics-enabled quantum engineering. We anticipate that these directions will continue to attract researchers to the field and, in addition to showcasing intriguing science, will enable unprecedented functionalities that enhance the efficiency of alternative information technologies and computational schemes.

Meterscale Strong Coupling between Magnons and Photons.

We experimentally realize a meterscale strong coupling effect between magnons and photons at room temperature, with a coherent coupling of ∼20 m and a dissipative coupling of ∼7.6 m. To this end, we integrate a saturable gain into a microwave cavity and then couple this active cavity to a magnon mode via a long coaxial cable. The gain compensates for the cavity dissipation, but preserves the cavity radiation that mediates the indirect photon-magnon coupling. It thus enables the long-range strong photon-magnon coupling. With full access to traveling waves, we demonstrate a remote control of photon-magnon coupling by modulating the phase and amplitude of traveling waves, rather than reconfiguring subsystems themselves. Our method for realizing long-range strong coupling in cavity magnonics provides a general idea for other physical systems. Our experimental achievements may promote the construction of information networks based on cavity magnonics.

Magnetic field-dependent shape anisotropy in small patterned films studied using rotating magnetoresistance.

Based on the electric rotating magnetoresistance method, the shape anisotropy of a Co microstrip has been systematically investigated. We find that the shape anisotropy is dependent not only on the shape itself, but also on the magnetization distribution controlled by an applied magnetic field. Together with micro-magnetic simulations, we present a visualized picture of how non-uniform magnetization affects the values and polarities of the anisotropy constants K1 and K2. From the perspective of potential appliantions, our results are useful in designing and understanding the performance of micro- and nano-scale patterned ferromagnetic units and the related device properties.

Remarkably enhanced red-NIR broad spectral absorption via gold nanoparticles: applications for organic photosensitive diodes.

For organic films, remarkably enhanced red-NIR broad spectral absorption was achieved via the incorporation of gold nanoparticles (AuNPs) using a simple and facile preparation. The relevant thermal evaporation method has produced size-controllable AuNPs in the range of 0-20 nm diameter. The potential use of localized surface plasmon resonance (LSPR) enhanced organic photosensitive diodes (OPDs) as sensitive broadband sensors was discussed in this context. Here we showed that, by combining organic heterojunctions with size-controllable plasmonic AuNPs, the efficiency of organic photodetectors could be increased by up to one order of magnitude, because of LSPR and scattering effects of the AuNPs. Fabricated OPD devices showed a large photoresponse under radiation from wavelengths between 650 and 830 nm, accompanied by a low power consumption profile. A schematic energy level model combined with theoretical simulation analysis was proposed to explain the experimental data. More importantly, to the best of our knowledge, this work demonstrated the broadest photosensitivity with high responsivity from AuNP-based photodetectors, proving the potential of AuNPs as a promising material for efficient optoelectronic devices.