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(Fig. 1). This is in striking opposition for standing waves but also for itinerant References with most magnetization reversal spin-waves. This should open avenues for 1. Loth, S., Baumann, S., Lutz, C. P., Eigler, D. M. & Heinrich, A. J. Science 335, 196–199 (2012). models, which consider that in such propagating information and transfer the 2. Khajetoorians, A. A. Science 339, 55–59 (2013). 12 ultrasmall structures, inhomogeneous concepts of magnonics to the atomic 3. Miyamachi, T. et al. Nature 503, 242–246 (2013). excitations are forbidden and that scale. Logical operations at the atomic 4. Spinelli, A., Bryant, B., Delgado, F., Fernández-Rossier, J. & 13 Otte, A. F. Nature Mater. 13, 782–785 (2014). magnetization reversal is only due to scale, as recently demonstrated , should 5. Heinze, S. et al. Science 288, 1805–1808 (2000). homogeneous fluctuations. also benefit from the use of spin waves, 6. Loth, S. et al. Nature Phys. 6, 340–344 (2010). These experiments mark a great step opening new perspectives in computing 7. Heinrich, A. J., Gupta, J. A., Lutz, C. P. & Eigler, D. M. Science ❐ 306, 466–469 (2004). towards future ultrahigh-density data- with atoms. 8. Hirjibehedin, C. F., Lutz, C. P. & Heinrich, A. J. Science storage technologies. Not only do they 312, 1021–1024 (2006). demonstrate the control of spin waves Stanislas Rohart is at the Laboratoire de 9. Hirjibehedin, C. F. et al. Science 317, 1199–1203 (2007). down to atomic length scales, but they Physique des Solides, Université Paris-Sud 10. Gao, C. L. et al. Phys. Rev. Lett. 101, 167201 (2008). 11. Prokop, J. et al. Phys. Rev. Lett. 102, 177206 (2009). also give insight to possible read and and CNRS, Bâtiment 510, 91405 Orsay cedex, 12. Kruglyak, V. V., Demokritov, S. O. & Grundler, D. J. Phys. D write processes using spin waves to assist France. Guillemin Rodary is at Laboratoire 43, 264001 (2010). magnetization switching. In the future, de Photonique et de Nanostructures, CNRS, 13. Khajetoorians, A. A., Wiebe, J., Chilian, B. & Wiesendanger, R. Science 332, 1062–1064 (2011). the ability to create spin waves in atomic Route de Nozay, 91460 Marcoussis, France. wires should efficiently be used not only e-mail: [email protected] Published online: 6 July 2014 MATERIAL WITNESS CUTTING-EDGE There can be few more mythologized and low-phosphorus mild or ancient materials technologies iron — to produce a surface that could than sword-making. The common be polished and etched to striking view — that ancient decorative effect. After twisting and had an extraordinary empirical grinding, the metal surface could grasp of how to manipulate acquire striped, chevron and sinuous microstructure to make the finest- patterns that were highly prized. quality blades — contains a fair A letter to a Germanic tribe in the amount of truth. Perhaps the most sixth century ad, complimenting remarkable example of this was them for the swords they gave to discovered several years ago: the near- the Ostrogothic king Theodoric, PHILIP BALL legendary Damascus blades used by conqueror of Italy, praised the Islamic warriors, which were flexible interplay of shadows and colours in laminated with other materials. yet strong and hard enough to cleave the blades, comparing the pattern to The prettiness of pattern the armour of Crusaders, contained tiny snakes. didn’t, however, have to compromise carbon nanotubes1. Formation of the But was it all about appearance? the sword’s strength, as — at least nanotubes was apparently catalysed Surely what mattered most to a warrior in later examples — the patterned by impurities such as vanadium in the was that his sword could be relied section was confined to panels in the steel, and these nanostructures assisted on to slice, stab and maim without central ‘’ of the blade, while the

the growth of cementite (Fe3C) fibres breaking? It seems not. Thiele et al. cutting edge was steel. All the same, that thread through the unusually commissioned an internationally here’s an example of how materials high-carbon steel known as wootz, renowned swordsmith to make use may be determined as much by making it hard without paying the pattern-welded rods for them using social as by technical and mechanical price of brittleness. traditional techniques and re-smelted considerations. From the Early to the Yet it seems that the skill of the medieval iron. In these samples the High Middle Ages, swords weren’t just swordsmith wasn’t directed purely at high-phosphorus component was iron or even primarily for killing people making swords mechanically superior. and not, as some earlier studies have with. For the Frankish warrior, the Thiele et al. report2 that the practice mistakenly assumed, steel. spear and axe were the main weapons; called , well established They subjected the samples to swords were largely symbols of power in swords from the second century ad mechanical tests that probed the and status, carried by chieftains, jarls to the early medieval period, was stresses typically experienced by a and princes but used only rarely. primarily used for decorative rather sword: impact, bending and buckling. Judging by the modern reproductions, than mechanical purposes and, unless In no cases did the pattern-welded they looked almost too gorgeous to used with care, could even have samples perform any better than stain with blood. ❐ compromised the quality of the blades. hardened and tempered steel. This Pattern welding involved the is not so surprising, given that References 1. Reibold, M. et al. Nature 444, 286 (2006). lamination and folding of two phosphoric iron itself has rather 2. Thiele, A., Hosek, J., Kucypera, P. & Dévényi, L. materials — high-phosphorus iron poor toughness, no matter how it is Archaeometry http://dx.doi.org/10.1111/arcm.12114 (2014).

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