0428同步年報-2021-全

082 ACTIVITY REPORT 2021 MVE effect in RE M 2 is strongly related to the 3d electrons, modifying the transition-metal sites can tune the thermal- expansion behavior. Xing and his co-workers recently reported the thermal-expansion behavior in Ho 2 (Fe, Co) 17 and discovered the SIV in Ho 2 Fe 16 Co 1 . The thermal expansion of a material can be characterized with various techniques, such as a dilatometer, X-ray diffraction and neutron powder diffraction. Neutron powder diffraction, among the three, is unique in simultaneously probing the lattice expansion and long- range magnetic ordering that is critical for specific groups of NTE or ZTE materials. The high-intensity neutron powder diffractometer, WOMBAT , which is capable of rapid data acquisition, has undertaken many proposals on NTE and ZTE materials. Measurements of neutron powder diffraction indeed provide critical experimental results for Ho 2 (Fe, Co) 17 compounds in this work, such as the magnetic structure ( Fig. 1(a) ), temperature dependence of the lattice parameters and the magnetic moments of Ho and Fe/Co sites ( Figs. 1(c), 1(e)–1(g) ). The experimental results match well the results from first-principle calculations. Greatly varied thermal-expansion behaviors have been observed in Ho 2 (Fe, Co) 17 with varied Co substitution, as shown in Fig. 2(a) . Ho 2 Fe 17 exhibits the NTE behavior below T C ~ 340 K and a typical positive thermal expansion (PTE) above T C . The Co-substituted Ho 2 Fe 15 Co 2 and Ho 2 Co 17 exhibit low and high-PTE behaviors, respectively. In between, the HoFe 16 Co shows a wide temperature range of ZTE, in which the variation of cell volume is less than 1 Å 3 and the thermal- expansion coefficient is of order 10 -6 K -1 , as shown in Fig. 2(b) . The work on the R 2 (Fe, Co) 17 compounds by Xing and his collaborators utilizes various experimental probes and first-principle calculations. 3 All these techniques together reveal the key role of the 3d bonding state in the thermal expansion upon the long-range magnetic ordering. In this work, Xing and his collaborators reported a record wide SIV temperature range among metallic compounds, from 3 to 461 K (Δ T = 458 K), almost twice the value of known metallic SIV. This research together with the flexibility and numerous R-Fe-Co alloy systems indicates great potential in the development of promising thermal expansion and related functional magnetic performances. (Reported by Chin-Wei Wang) This report features the work of Xianran Xing and his collaborators published in Phys. Rev. Lett. 127 , 055501 (2021). Fig. 2 : (a) Temperature dependence of relative unit-cell volume determined with NPD refinements from 3 to 650 K for Ho 2 (Fe, Co) 17 compounds; (b) apparent zero thermal expansion of compound Ho 2 Fe 16 Co determined with a thermal dilatometer from 100 to 520 K. The coefficients of thermal expansion are of order 10 -6 K -1 in the three temperature windows. [Reproduced from Ref. 3] ANSTO WOMBAT – High-intensity Powder Diffractometer • NPD • Condensed-matter Physics References 1. Y. Cao, K. Lin, Z. Liu, J. Hu, C.-W. Wang, X. Liu, E. Tereshi- na-Chitrova, K. Kato, Q. Li, J. Deng, J. Chen, H. Zhang, X. Xing, Inorg. Chem. 59 , 5247 (2020). 2. Y. Cao, K. Lin, Z. Liu, J. Hu, C.-W. Wang, E. Tereshina-Chi- trova, K. Kato, Q. Li, J. Deng, J. Chen, H. Zhang, X. Xing, Inorg. Chem. 59 , 11228 (2020). 3. Y. Cao, K. Lin, S. Khmelevskyi, M. Avdeev, K. M. Taddei, Q. Zhang, Q. Huang, Q. Li, K. Kato, C. C. Tang, A. Gibbs, C.-W. Wang, J. Deng, J. Chen, H. Zhang, X. Xing, Phys. Rev. Lett. 127 , 055501 (2021).