Abstract:
Geometrical frustration plays a major role in achieving diverse physical properties in quantum magnets such as superconductivity, magnetoelectric, multiferroic, Weyl semimetal, and Skyrmion. In this talk, I will first review our relevant research findings in the past few years (Taiwan and USA) [1-10]. Later, I will focus on the latest discovery of the title compound, Cu2OSeO3, which belongs to a new member of the CuO-CuCl2-SeO2 ternary system (Japan) [11].
A new polymorph of Cu2OSeO3 with the distorted kagome lattice was successfully obtained using the high-pressure synthesis technique (Cu2OSeO3-HP). Selected-area electron diffraction (SAED) and convergent-beam electron diffraction (CBED) measurements have been performed, and the space group was resolved as monoclinic P21/c. The structural analysis using X-ray and neutron powder diffraction datasets suggests that the tetrahedral Cu2+ clusters [similar to those in Cu2OSeO3 ambient-pressure phase (Cu2OSeO3-AP)] exist in Cu2OSeO3-HP but with three symmetry inequivalent sites. No structural change was observed between 1.5 K and the room temperature. Detailed magnetization measurements together with neutron powder diffraction refinements identify a canted noncollinear antiferromagnetic order in Cu2OSeO3-HP, resulting in a net ferromagnetic moment along the b-axis. Subsequently, the complex magnetic H-T phase diagram was established based on the temperature and field dependent magnetization data. The comparison of the local magnetic structure viewed along the distorted kagome lattice for Cu2OSeO3-AP and Cu2OSeO3-HP suggests that the partially released geometrical frustration by structural distortion strongly alters the magnetic order. Size of the refined ordered moment is ~1 μ_B in Cu2OSeO3-HP, indicating a large enhancement compared to that of Cu2OSeO3-AP.
References:
[1] H. C. Wu et al., Sci. Rep. 5, 13579 (2015).
[2] H. C. Wu et al., J. Phys. D: Appl. Phys. 48, 475001 (2015).
[3] H. C. Wu et al., Phys. Rev. B 95, 125121 (2017).
[4] H. C. Wu et al., J. Phys. D: Appl. Phys. 50, 265002 (2017).
[5] H. C. Wu et al., Mater. Today Phys. 8, 34 (2019).
[6] H. C. Wu et al., Phys. Rev. B 100, 245119 (2019).
[7] H. C. Wu et al., Mater. Today Phys. 12, 100189 (2020).
[8] L. Z. Deng# and H. C. Wu# et al., Proc. Natl. Acad. Sci. 117, 8783 (2020). (#Co-first author)
[9] H. C. Wu* et al., Phys. Rev. B 102, 075130 (2020). (*Corresponding author)
[10] H. C. Wu* et al., Phys. Rev. B 103, 104111 (2021). (*Corresponding author)
[11] H. C. Wu* et al., to be submitted. (*Corresponding author)