2020同步年報

TPS 45A Submicron Soft X-ray Spectroscopy • XAS • Materials Science, Condensed-matter Physics References 1. M. Yen, Y.-H. Lai, C.-Y. Kuo, C.-T. Chen, C.-F. Chang, Y.-H. Chu, Adv. Funct. Mater. 30 , 2004597 (2020). 2. Y. Bitla, C. Chen, H. C. Lee, T. H. Do, C. H. Ma, V. Q. Le, C. W. Huang, W. W. Wu, L. Chang, P. W. Chiu, Y. H. Chu, ACS Appl. Mater. Interfaces 8 , 32401 (2016). 3. S. Ke, J. Xie, C. Chen, P. Lin, X. Zeng, L. Shu, L. Fei, Y. Wang, M. Ye, D. Wang, Appl. Phys. Lett. 112 , 031905 (2018). 4. D. L. Ko, M. F. Tsai, J. W. Chen, P. W. Shao, Y. Z. Tan, J. J. Wang, S. Z. Ho, Y. H. Lai, Y. L. Chueh, Y. C. Chen, D. P. Tsai, L. Q. Chen, Y. H. Chu, Sci. Adv. 6 , eaaz3180 (2020). 5. J. Liu, Y. Feng, R. Tang, R. Zhao, J. Gao, D. Shi, H. Yang, Adv. Electron. Mater. 4 , 1700522 (2018). 018 ACTIVITY REPORT 2020 Skyrmions at Room Temperature The temperature range in which the skyrmion phase of Cu 2 OSeO 3 is stabilized has been significantly enhanced from a small range, 55−58.5 K, to a large range, 5−300 K, on applying pressures up to 42.1 GPa. A skyrmion state is a special state observed in non-centrosymmetric helimagnets that exhibit topolog- ically protected spin textures. The skyrmion state is considered prom- ising for information technology, ultrarapid spintronics and microwave devices because an extremely small current is required to modify its spin configuration. To facilitate skyrmion applications, one great challenge is to expand the region of magnetic field–temperature phase space of the skyrmion state. Researchers have now found that the temperature region for the skyrmion phase in bulk Cu 2 OSeO 3 can be greatly enhanced under ap- plied physical pressure. 1 The authors prepared single crystals of Cu 2 OSeO 3 ; after characterizing the structure at ambient pressure, they measured χ’ ac (H) T,P as a function of H at varied P up to 42.1 GPa and T up to 300 K, as shown in Fig. 1 . The H–T regions in which the skyrmion state occurs at selected pressures, for example 2.5, 7.9, 26.2 and 42.1 GPa, are shown in Figs. 1(a)–1(d) , respectively. Figure 1 clearly shows that the temperature region ( T A1 , T A2 ) for skyrmions (red shaded areas), or Δ T ≡ ( T A2 − T A1 ), has been expanded from 55 K − 58.5 K, that is, Δ T ∼ 3.5 K, Fig. 1 : ac susceptibility of Cu 2 OSeO 3 as a function of magnetic field at varied critical pressures: (a) 2.5 GPa, (b) 7.9 GPa, (c) 26.2 GPa, (d) 42.1 GPa. The evolution of the “dip figure” indicates that the temperature region for the possible skyrmion state expands under pressure. At 7.9 GPa, the upper limit of the temperature range, T A2 , increases to 300 K, the highest tempera- ture measured in this experiment. At 26.2 GPa, the lower limit of the temperature range, T A1 , extends to 5 K. With pressure increasing to 42.1 GPa, the “dip feature” becomes more pro- nounced while the temperature range remains between 5 to 10 K and 300 K. [Reproduced from Ref. 1] at ambient pressures to 5 K − 300 K), that is, Δ T > 290 K, at 42.1 GPa by lowering T A1 and raising T A2 to above 300 K via pressure. The extension of T A2 above 300 K above 7.9 GPa makes the skyrmion state accessible without the aid of liquid cryo- gen for device applications. At the same time, the field region (H A1 , H A2 ) or ΔH ≡