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Publications about this research: M.C. Langner, S. Roy, S.K. Mishra, Behavior Revealed by Two X-Ray Studies J.C.T. Lee, X.W. Shi, M.A. Hossain, Y.-D. Chuang, S. Seki, Y. Tokura, S.D. Kevan, and R.W. Schoenlein, Sometimes, the spins in a “Coupled Skyrmion Sublattices in magnetic material will form Cu2OSeO3,” Phys. Rev. Lett. 112, tiny swirls that can move 167202 (2014); J. Li, A. Tan, K.W. around like particles. The spins Moon, A. Doran, M.A. Marcus, A.T. Young, E. Arenholz, S. Ma, themselves stay put—it’s the R.F. Yang, C. Hwang, and Z.Q. Qiu, pattern that moves. These “Tailoring the topology of an quasiparticles have been artificial magnetic skyrmion,” Nat. dubbed “,” after Commun. 5, 4704 (2014). British physicist Tony Skyrme, Research conducted by: M.C. who described their mathe- Langner and R.W. Schoenlein matics in a series of papers in (Berkeley Lab); S. Roy, S.K. the early 1960s. Now, over 50 Mishra, J.C.T. Lee, X.W. Shi, M.A. years later, scientists are Hossain, Y.-D. Chuang, A. Doran, intrigued by the possibility that M.A. Marcus, A.T. Young, and E. skyrmions could play a key role Arenholz (ALS); S. Seki (RIKEN in spintronics—electronics that and Japan Science and Technology employ spin to carry and mani- Agency); Y. Tokura (RIKEN and Univ. of Tokyo); S.D. Kevan (ALS upulate information. At the and Univ. of Oregon); J. Li, A. Tan, ALS, two research groups have S. Ma, R.F. Yang, and Z.Q. Qiu recently published separate (Univ. of California, Berkeley); and studies in which soft x-rays K.W. Moon and C. Hwang (Korea reveal how skyrmions react to A skyrmion is an atom-sized whirlwind of magnetism, in which Research Institute of Standards external fields, laying the foun- the spins of charged particles form a vortex. In this image, the and Science). color scale—red for longer and blue for shorter vectors—shows dation for understanding and Research funding: U.S. Department eventually utilizing these fasci- that the magnetization is highest at the center of the skyrmion. of Energy (DOE), Office of Basic nating constructs. (Image by Matthew Langner) Energy Sciences (BES); National Although skyrmions act Science Foundation; National like particles (namely, baryons), Research Foundation of Korea; they are actually magnetic Add to this the discovery tron orbitals stabilize the and China Scholarship Council. vortices formed from the spins that skyrmions can be moved skyrmionic phase. Until now, Operation of the ALS is supported by DOE BES. of charged particles. Spin is a coherently over macroscopic the copper selenite skyrmions quantum property in which distances with a tiny electrical had only been observed with the charged particles act like current, and you have a strong scattering and trans- bar magnets rotating about an spintronic candidate. mission electron microscopy, axis that points either “up” A major breakthrough techniques that are insensitive or “down.” The discovery of came with the discovery of to electron orbitals. skyrmions in manganese sili- skyrmions in copper selenite In one skyrmion study cide generated much excite- because its magnetic proper- done at the ALS, researchers ment because their exotic ties can be controlled with an gathered element-specific, hedgehog-like spin texture is electric field. To achieve this orbital-sensitive electronic and topologically protected and, control, however, we must magnetic structural informa- therefore, extremely stable. understand how different elec- tion using resonant x-ray scat- Particles, Practically

Why do some particles decay while others do not? What is a particle, anyway? Physicists long ago moved beyond the idea of permanent, indivisible “atoms” of matter to increasingly abstract concepts such as wave-particle dualities and quan- tum field theories that treat particles as excited states in an underlying “particle” field. If these treatments were not quite as satisfying at an intuitive level, at least they worked, pre- dicting phenomena such as interference effects and limited particle lifetimes.

Skyrmions, the product of one such treatment, have been Soft x-ray diffraction images from copper selenide show five sets resurrected from particle to find new application as of dual-peak skyrmion structures, highlighted by the white ovals. quasiparticles in condensed matter physics, where they The dual peaks represent the two skyrmion sublattices that rotate emerge from complex interactions between spins, orbitals, with respect to each other. All peaks fall on an arc (white line) low dimensionality, and external fields. A key feature of mag- representing the constant amplitude of the skyrmion wave vector. netic skyrmions is that they are topologically protected: because their spin structures cannot be continuously deformed into other magnetic states, they don’t “decay.” The combination of this stability, their nanometer size, and the low magnetic and electric fields required for manipulating them makes skyrmions practical particles for spintronic applications and high-density information storage.

Skyrmion PEEM images after the application of an in-plane tering at Beamline 12.0.2, tions that can’t exist in mate- magnetic field pulse (skyrmion core annihilation process) for (a) N=0 optimized for coherent x-ray rials with a single magnetic and (b) and N=1. The central vortex is surrounded by out-of-plane scattering studies of magnetic lattice structure. nickel spins as indicated by the yellow symbols. A lower critical materials. They were able to In another study, a second field is needed to annihilate the core for N=0 compared to N=1. show that although skyrmions research group created artifi- act like magnetic particles, cial skyrmions in 30-nm-thick their origin in copper selenite cobalt disks on 30-monolayer to control the formation of the skyrmions (parallel). This is electronic and that tempera- nickel, all on a copper substrate. two states in this system. distinct behavior for the two ture can be used to move the This structure created two To study the skyrmions’ states suggests a topological skyrmions in either a clockwise magnetic regions: the area topological nature, the effect of the magnetic skyrmions or counter-clockwise direction. in/under the cobalt disk researchers annihilated the in the core annihilation process. They also found the unex- (in-plane magnetization), and skyrmions by applying an The exploration of the pected existence of two the surrounding nickel (out-of- in-plane magnetic pulse that world of magnetic skyrmions distinct skyrmion sublattices plane magnetization). This was pushed the core out of the disk, is just beginning, but it that rotate with respect to each important because skyrmions converting the vortex into a already reveals that these other, creating a moiré-like can be characterized by a simple magnetic domain. Photo- particle-like spin configura- pattern. Compared to materials skyrmion number (N) equal to 0 emission electron microscopy tions not only hold promise with a simpler magnetic struc- when the core and surrounding (PEEM) measurements at for ultracompact data storage ture, the sublattices provide for spins are parallel, and 1 when Beamline 11.0.1 revealed that and processing, but they may an extra degree of freedom to they are antiparallel. By applying N=1 skyrmions (antiparallel) also open up entirely new minimize the free energy. various out-of-plane magnetic required a higher critical field areas of study in the emerging This leads to magnetic excita- fields, the researchers were able for annihilation than N=0 field of quantum topology.

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