NSRRC Activity Report 2023

Neutron Science 087 Fig. 3 : Low energy side of spin wave dispersion at T = 1.5, 35, and 70 K using a cold triple axis spectrometer SIKA . These data allow the team to determine the exchange parameters J 1 and J 2 with high resolution. [Reproduced from Ref. 1] Their research delves into the complexities of the magnetic and crystal structures of Lu y Y 1−y MnO 3 , outlining how various compositions affect these structures. It discusses the temperature-dependent atomic positions of Mn and how these shifts relate to the magnetic ordering and trimerization of the system. The results indicate a subtle yet noticeable impact on the magnetic structure and behavior of the material depending on the temperature and the (Lu,Y) composition. This may help to further understand the underlying physics of 2D-THA systems. Particularly, their work has revealed that using two irreducible representations may be necessary to solve the magnetic structures of other 2D-THA systems. To understand the magnetic structures and dynamics further, inelastic neutron scattering studies were conducted using SIKA in ANSTO. These experiments allowed for a detailed investigation of the spin-wave dispersion and the magnetoelastic excitations. The team noted that the composition Lu 0.3 Y 0.7 MnO 3 was an ideal candidate to investigate these phenomena due to its near-ideal parameters for examining trimerization and frustrated magnetism. Furthermore, their study extensively discusses the spin- wave dispersion. The research showed that the trimerization effect upon cooling was not noted at the manganese atomic position x Mn , highlighted by changes in the nearest- neighbor exchange interaction as shown in Fig. 3 . This is referred to as “weak trimerization.” In summary, their research offers a detailed exploration of the weak trimerization observed in Lu y Y 1−y MnO 3 and its implications for understanding the materials’ magnetic and structural properties. Through comprehensive structural analysis and magnetic excitation studies, the research contributes valuable insights into the complex behaviors of 2D-THA systems, with broader implications for the field of condensed matter physics. (Reported by Shinichiro Yano) This report features the work of Shinichiro Yano and his collaborators published in Phys. Rev. B 107 , 214407 (2023). ANSTO SIKA – Cold Neutron Triple-axis Spectrometer ANSTO WOMBAT – High-intensity Powder Diffractometer • Neutron Inelastic Scattering • Materials Science, Condensed-matter Physics Reference 1. S. Yano, C.-W. Wang, J. S. Gardner, W.-T. Chen, K. Iida, R. A. Mole, D. Louca, Phys. Rev. B 107 , 214407 (2023).