Magnonics is a budding research field in nanomagnetism and nanoscience that addresses the use of spin waves (magnons) to transmit, store, and process information. The rapid advancements of this field during last one decade in terms of upsurge in research papers, review articles, citations, proposals of devices as well as introduction of new sub-topics prompted us to present the first Roadmap on Magnonics. This a collection of 22 sections written by leading experts in this field who review and discuss the current status besides presenting their vision of future perspectives. Today, the principal challenges in applied magnonics are the excitation of sub-100 nm wavelength magnons, their manipulation on the nanoscale and the creation of sub-micrometre devices using low-Gilbert damping magnetic materials and its interconnections to standard electronics. To this end, magnonics offers lower energy consumption, easier integrability and compatibility with CMOS structure, reprogrammability, shorter wavelength, smaller device features, anisotropic properties, negative group velocity, non-reciprocity and efficient tunability by various external stimuli to name a few. Hence, despite being a young research field, magnonics has come a long way since its early inception. This Roadmap asserts a milestone for future emerging research directions in magnonics, and hopefully, it will inspire a series of exciting new articles on the same topic in the coming years.

A fundamental form of magnon-phonon interaction is an intrinsic property of magnetic materials, the “magnetoelastic coupling.” This form of interaction has been the basis for describing magnetostrictive materials and their applications, where strain induces changes of internal magnetic fields. Different from the magnetoelastic coupling, more than 40 years ago, it was proposed that surface acoustic waves may induce surface magnons via rotational motion of the lattice in anisotropic magnets. However, a signature of this magnon-phonon coupling mechanism, termed magneto-rotation coupling, has been elusive. Here, we report the first observation and theoretical framework of the magneto-rotation coupling in a perpendicularly anisotropic film Ta/CoFeB(1.6 nanometers)/MgO, which consequently induces nonreciprocal acoustic wave attenuation with an unprecedented ratio of up to 100% rectification at a theoretically predicted optimized condition. Our work not only experimentally demonstrates a fundamentally new path for investigating magnon-phonon coupling but also justifies the feasibility of the magneto-rotation coupling application.

We report the experimental observation of collective picosecond magnetization dynamics in [Co/Pd] 8 multilayers with perpendicular magnetic anisotropy. The precession frequency shows large and systematic variation from about 5 GHz to about 90 GHz with the decrease in the Co layer thickness from 1.0 nm to 0.22 nm due to the linear increase in the perpendicular magnetic anisotropy. The damping coefficient α is found to be inversely proportional to the Co layer thickness and a linear relation between the perpendicular magnetic anisotropy and α is established. We discuss the possible reasons behind the enhanced damping as the d-d hybridization at the interface and spin pumping.These observations are significant for the applications of these materials in spintronics and magnonic crystals. a) Electronic mail: abarman@bose.res.in

Magnonics addresses the physical properties of spin waves and utilizes them for data processing. Scalability down to atomic dimensions, operation in the GHz-to-THz frequency range, utilization of nonlinear and nonreciprocal phenomena, and compatibility with CMOS are just a few of many advantages offered by magnons. Although magnonics is still primarily positioned in the academic domain, the scientific and technological challenges of the field are being extensively investigated, and many proof-of-concept prototypes have already been realized in laboratories. This roadmap is a product of the collective work of many authors that covers versatile spin-wave computing approaches, conceptual building blocks, and underlying physical phenomena. In particular, the roadmap discusses the computation operations with Boolean digital data, unconventional approaches like neuromorphic computing, and the progress towards magnon-based quantum computing. The article is organized as a collection of sub-sections grouped into seven large thematic sections. Each sub-section is prepared by one or a group of authors and concludes with a brief description of current challenges and the outlook of further development for each research direction.

Despite significant technological advances in miniaturization and operational speed, modern electronic devices suffer from unescapably increasing rates of Joule heating and power consumption. Avoiding these limitations sparked the quest to identify alternative, chargeneutral information carriers. Thus, spin waves, the collective precessional motion of spins in permanent magnets, were proposed as a promising alternative system for encoding information. In order to surpass the speed, efficiency, functionality and integration density of current electronic devices, magnonic devices should be driven by electric-field induced methods. This review highlights recent progress in the development of electric-fieldcontrolled magnonic devices, including present challenges, future perspectives and the scope for further improvement. S pin waves (SWs) are the dynamic eigen modes of magnetically ordered systems, such as ferromagnetic (FM) metals 1,2 , ferrimagnetic insulators 3,4 and antiferromagnets 5. In other words, SWs are phase coherent collective precessional motion of ordered magnetic spins 6 (Fig. 1a). These SWs may serve as a potential information carrier in future microwave signalprocessing devices, by using its amplitude, phase, and polarization, at significantly lower power consumption as SWs are not associated with translational motion of electronic charges 4,7. Therefore, SWs can be used as an alternative to modern charge current-based complementary metal-oxide-semiconductor (CMOS) technology, which is now suffering from increased rate of power consumption due to Joule heating. The quanta of SWs are called "magnon". Following this name, a new research field, known as "magnonics" 6,8 , is rapidly developing. When magnonics meets spintronics, the field is known as magnon spintronics 9. The aim of magnonics is to control and manipulate SW properties so that they can be utilized in future spintronics technology 8,9. Apart from lower energy consumption, another advantage of SWs is that they can have wide variety of wavelengths ranging from few tens of micrometer down to few tens of nanometer with the corresponding frequency ranging from few Gigahertz to few Terahertz, which can be even controlled by tuning various internal and external parameters, such as saturation magnetization, various magnetic anisotropies, magnetostatic interactions, exchange interaction, magnetic field, and electric field 8,10,11. Although, SWs have much smaller group