The Next Wave

editorial The next wave Spin waves look poised to make a splash in data processing. Even before its discovery in 1897, control of appropriate materials, and the need of the electron had already played a role in for advanced nanoscience techniques to a technological revolution: electric power generate, manipulate and detect magnons enabled the mass-production manufacturing on the nanometre scale. But recent methods of the second industrial revolution demonstrations, such as the realization of in the nineteenth century. Levels of its a magnon transistor, highlight the progress manipulation have now reached such highs being made. that the technologies that pervade our daily To expand the set of materials capable lives would surely seem fanciful to the of hosting magnons, artificial crystals are scientists who first probed this elementary being used. In much the same way that particle. Now the world looks set to welcome photonic crystals exhibit tailored band a new way of exploiting the electron, in the structures for electromagnetic waves, form of magnonics. certain magnonic crystals can modify the The electron charge is firmly established band structure for magnons. Modulation is as the information carrier of choice for achieved in such crystals by varying their modern technologies. But what of its second magnetic properties On page 487 of this elementary property, spin? Despite being issue, Marc Vogel and colleagues show how discovered just ten years after the electron reconfigurable magnonic crystals can be charge was first measured, spin remains a created in an insulating ferrimagnet using relative passenger in information-processing all-optical methods. technologies. But its presence could The potential for using such techniques revolutionize these technologies, and in more in wireless communication technologies ways than one. OTTE OF SANDER COURTESY IMAGE is examined by Dirk Grundler in a The electron spin actually underpins Commentary on page 438. Coupling magnetic-storage technologies, with ordered materials using the collective electromagnetic waves to mechanical magnetic ‘bits’ encoded in the direction of precessional motion of spins. As each waves allowed for wireless communication a material’s magnetization, which reflects individual spin precesses on its given technologies to be drastically miniaturized. the behaviour of a collection of spins. What position, spin-wave propagation occurs Grundler discusses how magnonics could distinguishes spin from charge is that there without electron charges being displaced. not only provide wireless technologies that are two possible values, say 0 and 1, for One can therefore envisage a device where are small, but also reprogrammable. particles that have a spin of 1/2, such as an input voltage is converted into a spin As one might expect, the magnonics the electron. An intrinsic property capable wave, some wave-based computation and spintronics communities are closely of existing in multiple states sounds like is performed, and then the wave is intertwined. And as magnons can be the ideal candidate for logic operations. converted back into a voltage. There converted into electron-carried spin and Moreover, the manipulation of spins are several advantages to such a device, charge currents, circuits could be developed alleviates the losses associated with moving including parallel data processing on whose individual components utilize the charges, such as Joule heating. So why different wave frequencies, low power strength of the different spintronic, charge aren’t information-processing technologies consumption, and non-Boolean computing or magnonic elements. Andrii Chumak utilizing this property? It’s certainly not for algorithms — enabled by the additional and colleagues survey this topic in a want of trying. degree of freedom provided by the phase of Review Article on page 453. They discuss the Efforts to use spins for both data storage the waves. generation and manipulation of magnons, and information processing are a focus The field of research that aims to the mechanisms and progress on converting for many researchers in the spintronics exploit spin waves is known as magnonics, between magnon currents and spin and community. The field of spintronics grew which refers to the quantized version charge currents, and recent experimental out of the discovery of spin-dependent of spin waves: magnons. In this issue of advances that are laying the foundations for electron transport during the 1980s1 and is Nature Physics, we take a close look at magnon-based computing. concerned with using magnetic and electric the advances, prospects and challenges of As this Focus helps to illustrate, spin can fields to manipulate spins. Although many developing information processing and be used in technologies in more ways than logic devices based on spintronics are wireless communication technologies based one. And although magnonic devices have still in the development stages, some have on spin waves. some catching up to do if they are to emulate already reached the market. But there are Although spin waves were discovered their spintronic counterparts, they finally opportunities for technologies that go beyond decades before spin-dependent look set to be in the race. ❐ electron-carried charge and spin currents. transport effects, magnonic devices are It was proposed back in the 1930s2, and yet to reach the same heights as their References 3 1. Johnson, M. & Silsbee, R. H. Phys. Rev. Lett. 55, 1790 (1985). experimentally observed in 1950s , that spintronic counterparts. This progress 2. Bloch, F. Z. Physik 61, 206–219 (1930). waves could be excited in magnetically has perhaps been hindered by the lack 3. Brockhouse, B. N. Phys. Rev. 106, 859 (1957). NATURE PHYSICS | VOL 11 | JUNE 2015 | www.nature.com/naturephysics 437 © 2015 Macmillan Publishers Limited. All rights reserved.

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