NSRRC Activity Report 2022

082 NSRRC ACTIVITY REPORT 2022 in a vdW AFM structure; this experiment may contribute to the understanding and tunability of 2D magnet materials and stimulate future developments in 2D AFM spintronics. (Reported by Chin-Wei Wang) This report features the work of Wenyun Yang and his collaborators published in Adv. Mater. 32 , 2001200 (2020) and Adv. Funct. Mater. 32 , 2106592 (2022). ANSTO ECHIDNA – High-resolution Powder Diffractometer • NPD • Materials Science, Condensed-matter Physics References 1. Y. Peng, S. Ding, M. Cheng, Q. Hu, J. Yang, F. Wang, M. Xue, Z. Liu, Z. Lin, M. Avdeev, Y. Hou, W. Yang, Y. Zheng, J. Yang, Adv. Mater. 32 , 2001200 (2020). 2. Y. Peng, Z. Lin, G. Tian, J. Yang, P. Zhang, F. Wang, P. Gu, X. Liu, C.-W. Wang, M. Avdeev, F. Liu, D. Zhou, R. Han, P. Shen, W. Yang, S. Liu, Y. Ye, J. Yang, Adv. Funct. Mater. 32 , 2106592 (2022). Field-Induced Magnetic Ordering in a Tetrahedral Sublattice with Strong Magnetic Anisotropy Neutron powder diffraction is a powerful tool for studying magnetic properties in extreme sample environments. G eometric frustration in condensed matter systems is a phenomenon in which competing forces act on atoms reside on a regular lattice. Because of the frustration in the geometry, such a system exhibits degenerate ground states, preventing entrance into the long-range order phase. An example is geometrically frustrated antiferromagnets, where antiferromagnetic couplings with neighboring spins cannot be satisfied simultaneously. Pyrochlore compounds, with corner-sharing tetrahedral sublattices, are the most well-known and studied geometrically frustrated systems and undertake various magnetic phases. On the basis of degenerate ground states, a perturbation, such as a dipolar interaction, stabilizes spin ice behavior in Ho 2 Ti 2 O 7 and Dy 2 Ti 2 O 7 . Likewise, the conduction electron-mediated coupling, namely the Ruderman–Kittel–Kasuya–Yosida (RKKY) interaction, can serve as perturbation, causing novel magnetic phases in intermetallic compounds composed of geometrically frustrated sublattices. Ho 5 Co 6 Sn 18 is one example. Chin-Wei Wang (NSRRC) and co-workers reported comprehensive neutron scattering results for this compound. Two distinct crystallographic Ho sites, Ho(1) and Ho(2), exist in Ho 5 Co 6 Sn 18 . Both sublattices contain tetrahedral arrangements and can be magnetically frustrated. Each Ho(1) atom has 12 adjacent Ho(1) atoms, forming edge- sharing tetrahedrons. Conversely, the Ho(2) 4 tetrahedra are somewhat isolated; Ho(2) 4 units are separated by Ho(1) atoms and together form a rock salt structure. No significantmagnetic order exists in their magnetometry, while their heat capacity exhibit a peak at ~3.4 K, that is closed to the superconducting gap of tin metal. The temperature dependent magnetic peak intensity is measured on SIKA, that indicates the 3.4 K peak in heat capacity is associated to the long-range magnetic order. The data for neutron powder diffraction (NPD) performed at 1.5 K on ECHIDNA indicate a ferromagnetic structure on the Ho(1) sublattice and no ordered moment on the Ho(2) sublattice. A further investigation at the ultralow temperature of 60 mK demonstrated the magnetic order of Ho(2) spins; the Ho(2) spins on a Ho(2) 4 tetrahedron were (Mx, My, 0), (−Mx, −My, 0), (My, −Mx, 0), and (−My, Mx, 0). A 2-in-2-out configuration that is analogous to the magnetic Fig. 2 : Temperature-pressure magnetic phase diagram of CrPS 4 determined from magnetometry data. The blue region between the AFM ac and AFM b phases represents the coexistence of both phases (AFM ac + AFM b ), reflecting the first-order nature of the magnetic phase transition. [Reproduced from Ref. 2]