Magnetic skyrmions, vortex-like topological spin textures, have attracted much attention in terms of both fundamental physics and spintronics applications. Thus far, skyrmions have been observed in thin-film multilayers with interfacial Dzyaloshinskii-Moriya interaction (DMI) and structurally-chiral magnets with bulk DMI. Recently, bulk-DMI-induced skyrmions have been observed above room temperature in Co-Zn-Mn alloys with a β-Mn-type chiral structure . In most chiral magnets, however, skyrmions exist as a thermodynamically equilibrium state only in a narrow temperature and magnetic field region just below the magnetic transition temperature Tc. The limited region of the stable skyrmions is unfavorable for applications.
Here, we focused on β-Mn-type Co9Zn9Mn2 (Tc ~ 400 K) and performed small-angle neutron scattering, magnetic susceptibility and Lorentz transmission electron microscope measurements. We demonstrated that skyrmions persist over almost the whole temperature region below 400 K as a long-lived metastable state by performing a conventional field-cooling process. Once created, metastable skyrmions survive above room temperature after removal of magnetic field . These findings exemplify the topological robustness of the once-created skyrmions and provide a significant step toward applications of skyrmions in bulk chiral magnets.
In the presentation, we will discuss the details of the above observations, and also show novel skyrmion states in Co-Zn-Mn alloys with other chemical compositions.
 Y. Tokunaga et al., Nat. Commun. 6, 7638 (2015).
 K. Karube et al., Phys. Rev. Mater. 1, 074405 (2017).
Kosuke Karube, Jonathan S. White, Marek Bartkowiak, Daisuke Morikawa, Xiuzhen Yu, Akiko Kikkawa, Yusuke Tokunaga, Takahisa Arima, Henrik M. Rønnow, Yoshinori Tokura, and Yasujiro Taguchi, "Robust magnetic-field-free skyrmions above room temperature in a bulk chiral magnet
(Conference Presentation)," Proc. SPIE 10732, Spintronics XI, 107323H (Presented at SPIE Nanoscience + Engineering: August 23, 2018; Published: 18 September 2018); https://doi.org/10.1117/12.2319900.5836437162001.
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