NSRRC Activity Report 2022

Neutron Science 083 ordered phases in pyrochlore compounds. At 60 mK, an overall noncollinear spin structure was realized. Ho(1) spins ordered ferromagnetically along the c -axis, and Ho(2) spins were located in the ab plane. The strong magnetic anisotropy indicated by the nonsaturated character of M(H) suggests the necessity for further investigation into the magnetic field effect of WOMBAT . 1 Figure 2 shows the effect of the magnetic field on the magnetic structure at 2 K. The magnetic space group was not altered by a magnetic field of up to 90 kOe. The order moment of Ho(1) increased linearly to the magnetic field, whereas the fluctuating Ho(2) moment was induced substantially. As shown in Fig. 2(b) , not only was the ferromagnetic c -component induced, but the antiferromagnetic in-plane component also increased. Thus, Ho(2) maintained an angle of approximately 54° to the ab plane between 10 and 90 kOe. This can be attributed to the balance between the in-plane magnetic anisotropy of Ho(2) and the external field, which reduced spin fluctuation rather than deflecting from the easy plane. In summary, the ferromagnetic coupling, J Ho(1)−Ho(1) , was strong, and long-range magnetic order developed on the Ho(1) sublattice, causing Ho(2) to be released. The magnetic properties of the Ho(2) sublattice were affected by both the antiferromagnetic J Ho(2)−Ho(2) couplings and in-plane magnetic anisotropy. The high penetration of neutron beams enables the investigation of magnetic properties at an ultralow temperature and with a strong magnetic field. These experiments were undertaken at the neutron facility of Australian Centre for Neutron Scattering at Australia's Nuclear Science and Technology Organisation (ACNS, ANSTO), and are available to Taiwanese researchers. (Reported by Chin-Wei Wang) This report features the work of Chin-Wei Wang and his collaborators published in Phys. Rev. B 105 , 104429 (2022). ANSTO WOMBAT – High-intensity Powder Diffractometer ANSTO ECHIDNA – High-resolution Powder Diffractometer ANSTO SIKA – Cold Neutron Triple-axis Spectrometer • NPD, Inelastic Neutron Scattering • Condensed-matter Physics, Materials Science Reference 1. C.-W. Wang, S. K. Karna, S.-I. Yano, C.-H. Lee, M. Avdeev, C. S. Lue, C. N. Kuo, Phys. Rev. B 105 , 104429 (2022). Fig. 1 : (a) Magnetic structure at 60 mK shows the Ho(1) spin pointing along the c -axis and the Ho(2) spins located in the ab plane. Panels (b)–(e) show the magnetic structure viewed along the c -axis sliced into four layers: (b) z = [0: 0.25], (c) z = [0.25: 0.5], (d) z = [0.5: 0.75], and (e) z = [0.75: 1]. [Reproduced from Ref. 1] Fig. 2 : Refined magnetic moments from the NPD patterns collected under various fields and temperatures. (a) Modulus of the magnetic moments of Ho(1) and Ho(2). (b) M x , M y , and M z components of Ho(2). (c) Angle between Ho(2) and the ab plane. [Reproduced from Ref. 1]