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 is 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.

The application of Brillouin light scattering to the study of the spin-wave spectrum of one- and two-dimensional planar magnonic crystals consisting of arrays of interacting stripes, dots and antidots is reviewed. It is shown that the discrete set of allowed frequencies of an isolated nanoelement becomes a finite-width frequency band for an array of identical interacting elements. It is possible to tune the permitted and forbidden frequency bands, modifying the geometrical or the material magnetic parameters, as well as the external magnetic field. From a technological point of view, the accurate fabrication of planar magnonic crystals and a proper understanding of their magnetic excitation spectrum in the gigahertz range is oriented to the design of filters and waveguides for microwave communication systems.

The Dzyaloshinskii-Moriya interaction (DMI), one of the origins of chiral magnetism, is currently attracting considerable attention in the research community focusing on applied magnetism and spintronics. For future applications, an accurate measurement of its strength is indispensable. Here the state of the art of measurement techniques involving the coefficient of the Dzyaloshinskii-Moriya interaction, the DMI constant $D$, is reviewed, with a focus on systems where the interaction arises from the interface between two materials (i.e., the interfacial DMI). An overview of the experimental techniques, as well as their theoretical background and models for the quantification of the DMI constant, is given. The measurement techniques are divided into three categories: (a) domain-wall-based measurements, (b) spin-wave-based measurements, and (c) spin-orbit torque-based measurements. The advantages and disadvantages of each method are analyzed, and $D$ values at different interfaces are compared. The review aims to obtain a better understanding of the applicability of the different techniques to various stacks and of the origin of apparent disagreements among literature values.

The magnetic normal modes of nanometric magnetic disks are calculated using a recently developed, hybrid micromagnetic method. The method is based on the subdivision of a particle into small cells and the development of a “dynamical matrix” that contains the restoring torques acting on the magnetization of each cell. The method includes dipolar, Zeeman, and exchange interactions. The results of these calculations are used to interpret the spin wave spectra measured by Brillouin scattering in an array of nanometric Permalloy™ disks over a wide range of applied fields encompassing both the vortex and saturated states.

Magnetization dynamics of dipolarly coupled nanowire arrays has been studied by Brillouin light scattering. Measurements performed in uniformly magnetized wires as a function of the transferred wave vector demonstrated the existence of several discrete collective modes, propagating through the structure with a periodic dispersion curve encompassing several Brillouin zones relative to the artificial spatial periodicity. This experimental evidence has been quantitatively explained by a theoretical model which permits the calculation of the dispersion relation for collective modes in patterned arrays through the numerical solution of an eigenvalue problem for an integral operator.