Dipolar superferromagnetism with reentrant low-temperature superspin glass behavior is observed on a randomly distributed ferromagnetic nanoparticle systems in discontinuous metal-insulator multilayers ͓Co 80 Fe 20 (t)/Al 2 O 3 ͑3 nm͔͒ 10 with nominal thickness 1.1рtр1.3 nm by use of ac susceptometry and dc magnetometry. At tϭ1.0 nm, superspin glass-like freezing is evidenced by the criticality of dynamic and nonlinear susceptibilities.

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.

A theoretical analysis has been done of the effects of granule size, shape, orientation, and concentration and the temperature effects on the ferromagnetic resonance (FMR) field Hr in granular thin films. The granular CoxAg1−x thin films with 0.2<x<0.85 (the volumetric filling factor 0.17<f<0.83) were prepared by electron-beam oblique coevaporation. Our room temperature FMR data show an abrupt change in the Hr(f) dependence at f=fp≈0.3, the percolation point for this system (as evidenced from the magnetization and magnetoresistance measurements). This change is associated to the development of great clusters [ferromagnetic (FM) phase] beside single granules [superparamagnetic (SPM) phase] at f>fp. For the Co–Ag system, persistence of a considerable SPM fraction is revealed by the superconducting quantum interference device data up to the highest f, and the effect at f=fp consists in a discontinuous jump of the Hr(f) slope. Otherwise, the FMR data for granular Fe–SiO2 films reveal a discontinuous jump in Hr itself at f≈0.28. The latter can indicate a 1st kind-like magnetic percolation transition in that material. Thus FMR studies can effectively probe the internal structural processes in granular magnetic systems.

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