Magnonics is a young field of research and technology emerging at the interfaces between the study of spin dynamics, on one hand, and a number of other fields of nanoscale science and technology, on the other. We review the foundations and recent achievements in magnonics in view of guiding further progress from studying fundamental magnonic phenomena towards applications. We discuss major challenges that have to be addressed in future research in order to make magnonics a pervasive technology.

Ultrafast non-thermal manipulation of magnetization by light relies on either indirect coupling of the electric field component of the light with spins via spin-orbit interaction or direct coupling between the magnetic field component and spins. Here we propose a scenario for coupling between the electric field of light and spins via optical modification of the exchange interaction, one of the strongest quantum effects with strength of 103 Tesla. We demonstrate that this isotropic opto-magnetic effect, which can be called inverse magneto-refraction, is allowed in a material of any symmetry. Its existence is corroborated by the experimental observation of terahertz emission by spin resonances optically excited in a broad class of iron oxides with a canted spin configuration. From its strength we estimate that a sub-picosecond modification of the exchange interaction by laser pulses with fluence of about 1 mJ cm−2 acts as a pulsed effective magnetic field of 0.01 Tesla.

The study of collective spin excitations in magnetically ordered materials (so-called spin waves and the associated quasi-particles—magnons) has a successful history of more than 60 years. Recently, it has re-emerged in a new aspect under the name of magnonics, although the exact definition of its scope is still a subject for debate. However, it is widely accepted that the recent renaissance of interest in spin waves has been driven by three major factors: the rapid advance of nanotechnology, the development of new experimental techniques for studying high-frequency magnetization dynamics and the promise of a new generation of functional magnetic field controlled devices in which spin waves (magnons) would be employed, in particular to carry and process information. Furthermore, the growing interest in man-made 'crystals', such as those already realized in photonics, electronics and plasmonics, has served as a further strong catalyst for the development of so-called magnonic crystals. Magnonics as a research field is currently gaining momentum, attracting more and more researchers from various sub-fields of magnetism, materials science, microwave engineering, and beyond. Hence, it is timely to define the state of the art of this exciting research field emerging at the interface between magnetism and nanoscience. The first magnonics conference, entitled 'Magnonics: From Fundamentals to Applications' was held in Dresden in August 2009, sponsored by the visitor programme of the Max Planck Institute for the Physics of Complex Systems (MPIPKS). The event was a great success, having achieved its main aim of forming a community of magnonics researchers. It brought together both experts who held worldwide leading positions in nanomagnetism and spin wave research, and younger researchers just entering the field. The research results presented ranged from fundamental magnonic properties to their application in information technologies. The main scientific result of the conference in the broader sense was the emergence of magnonics as a sister field in the family of functional nanomaterials that also includes electronics, photonics, phononics, plasmonics etc. The presentations helped to define the state of the art and to highlight perspectives of the field. The conference led to the idea of publishing this cluster of papers aimed at reviewing the history of and the recent progress in magnonics. The cluster begins with a contribution from Kruglyak et al who aim to define the general scope and concepts of magnonics as a research field [1]. Serga et al review the state of the art in studies of spin waves in yttrium iron garnet (YIG) samples, which—due to the exceptionally low magnetic losses—have been the most popular and extensively investigated so far [2]. Gubbiotti et al review their recent experiments in which the magnonic band gap spectrum was observed in planar metallic magnonic crystals with submicrometre periods [3]. Kim demonstrates how numerical simulations can be used to investigate a wide range of magnonic phenomena in truly magnetic nanostructures, which still remains a challenge for modern experiments [4]. Finally, Khitun et al discuss the prospects and challenges for the creation of magnonic logic devices [5]. As with any dynamic research field, the reviews are inevitably incomplete. Nonetheless, we hope that the cluster of papers will stimulate further progress in magnonics and will provide a useful starting point for researchers newly entering this challenging and exciting research field. References [1] Kruglyak V V, Demokritov S O and Grundler J 2010 J. Phys. D: Appl. Phys. 43 264001 [2] Serga A A, Chumak A V and Hillebrands B 2010 J. Phys. D: Appl. Phys. 43 264002 [3] Gubbiotti G, Tacchi S, Madami M, Carlotti G, Adeyeye A O and Kostylev M 2010 J. Phys. D: Appl. Phys. 43 264003 [4] Kim S-K 2010 J. Phys. D: Appl. Phys. 43 264004 [5] Khitun A, Bao M and Wang K L 2010 J. Phys. D: Appl. Phys. 43 264005

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.

We use time resolved scanning Kerr microscopy and analytical and numerical calculations to demonstrate coupling of uniform global microwave field to propagating spin waves for emerging magnonic architectures. The coupling is mediated by the local dynamic dipolar field produced by the magnetization of a resonantly driven all-metallic magnetic microwave-to-spin-wave transducer. The local dipolar field can exceed that of the incident microwave field by one order of magnitude. Our numerical simulations demonstrate the ability of the transducer to unidirectionally emit coherent exchange spin waves of nanoscale wavelengths with the emission direction programmed by the magnetic state of the transducer.

We have used time resolved scanning Kerr microscopy to image collective spin wave modes within a 2D array of magnetic nanoelements. Long wavelength spin waves are confined within the array as if it was a continuous element of the same size but with effective material properties determined by the structure of the array and its constituent nanoelements. The array is an example of a magnonic metamaterial, the demonstration of which provides new opportunities within the emerging field of magnonics.

The picosecond magnetization dynamics of arrays of square Ni 88 Fe 12 /Co 80 Fe 20 bilayer nanoelements were studied by optical pump-probe measurements. Experimentally observed modes were found to fall upon two branches, with a crossover from the high-to low-frequency regime as the element size was reduced to less than 220 nm. Micromagnetic simulations revealed that the branches are associated with center and edge modes. The edge mode is found to dominate as the element size is reduced so that the magnetic response to a pulsed field becomes less spatially uniform. DOI: 10.1103/PhysRevB.71.220409 PACS number͑s͒: 75.40.Gb, 75.30.Ds, 75.50.Ss, 78.47.ϩp Increased storage densities in magnetic data storage technology require the use of nanoscale magnetic elements.1 A full understanding of the spin-wave ͑SW͒ spectrum is also essential if higher data rates are to be achieved, for example, by the implementation of ultrafast precessional switching. 2Spatial confinement leads to quantized modes with frequency and spatial character that have a complicated dependence upon the exchange interaction and nonuniform demagnetizing field within the element.3-8 Interest in switching processes has led to the development of experimental techniques that allow SW excitations to be observed within the time domain.9,10 Although a number of studies have been performed upon microscale elements, nanoscale elements have not yet been extensively explored. Continued progress therefore requires the study of high-quality arrays of elements of identical shape and size. 3,5,8,11 In this paper, time-resolved scanning Kerr microscopy ͑TRSKM͒ measurements 9 are used to investigate magnetization dynamics in arrays of magnetic elements with size ranging from 64 to 630 nm. Specifically, we study elements with a composition similar to that used in the free layer of a spin or tunnel valve recording sensor or a magnetic random access memory element. Using the TRSKM as a probe of the magnetization dynamics at the center of an array, we record its time-dependent response to a pulsed magnetic field. We show that the measured precession undergoes a crossover to a lower-frequency regime as the element size is reduced below a certain value. Numerical simulations performed with the object oriented micromagnetic framework ͑OOMMF͒ ͑Ref. 12͒ reproduce the observed variations in the mode frequencies and lead to the surprising conclusion that the magnetic response of the smallest nanoscale elements is less, rather than more, spatially uniform.A Ta͑50 Å͒ /Co 80 Fe 20 ͑10 Å͒ /Ni 88 Fe 12 ͑27 Å͒ /Ta͑100 Å͒ film was sputtered onto a Si substrate and patterned, using a combination of electron-beam lithography and ion milling, into square arrays of square elements. The element lengths ͑edge-to-edge separations͒ were 630 ͑37.5͒, 425 ͑21.9͒, 220 ͑95͒, 120 ͑37.5͒, and 64 ͑48.4͒ nm, while the length of each array was about 4 m. Scanning electron microscope images 13 showed that the corners of the 64 and 120 nm elements were slightly rounded. The compositions of the Ni 88 Fe...

An experimental scheme for studying spin wave propagation across thin magnetic film samples is proposed. The scheme is based upon the creation of picosecond pulses of strongly localized effective magnetic field via ultrafast optical irradiation of a specially deposited exchange bias or exchange spring layer. The spin waves are excited near the irradiated surface before propagating across the thickness of the sample. They are then detected near the other surface either within the finite optical skin depth using the linear magneto-optical Kerr effect in metallic samples or by the magnetic second harmonic generation. The experiment can facilitate investigations of propagating spin waves with wavelengths down to several nanometers and frequencies in excess of hundreds of Gigahertz. An experiment upon a periodically layered nanowire (a finite cross-section magnonic crystal) is numerically simulated, although the sample might equally well be a continuous film or an array of elements (e.g. nanowires) that either have uniform composition or are periodically layered as in a magnonic crystal. The experiments could be extended to study domain wall-induced spin wave phase shifts and can be used for the creation of spin wave magnetic logic devices. r