A first-order phase transition of anti-helical structure in CuB₂O₄

Chun-Hao Lai^1*, Shin-ichiro Yano², Wei-Tin Chen³, Chao-Hung Du¹

¹Department of Physics, Tamkang University, New Taipei City 25137, Taiwan
²National Synchrotron Radiation Research Center, Hsinchu 300092, Taiwan
³Center for Condensed Matter Sciences, National Taiwan University, Taipei 106319, Taiwan

* Presenter:Chun-Hao Lai, email:mars820511@gmail.com

The copper metaborate CuB₂O₄ (CBO) has been reported as a chiral helimagnet (CHM), which exhibits a continuous phase transition into chiral magnetic soliton lattice (CSL) by the application of a magnetic field. The tunable, as well as topological nature of the CSL, brings about significant magnetism for the application of modern spintronic devices. All these phenomena arise from the competition between Dzyaloshinskii–Moriya (DM) interaction and ferromagnetic (FM) coupling. According to symmetry discussion and representation analysis, CHM only exists in 52 chiral space groups with only proper rotations. However, the space group of CBO, I-42d, does not belong to one of them. We proposed a new model of the submitted anti-helical structure, which includes a DM interaction and an antiferromagnetic (AFM) coupling among spin-1/2 Cu²⁺ ions. By the Monte Carlo method, we simulated the magnon excitation of the XY spin model of CBO and compared the results with the reference. Furthermore, a phase transition between different incommensurate (ICM) phases has been discovered via magnetic field-dependent neutron scattering, and the presence of metastable states implies the transition is discontinuous that agrees with the magnetic hysteresis loop of the magnetization.

Keywords: Chrial Helimagnet, Chrial Soliton Lattice, Dzyaloshinskii–Moriya interaction, Spin Wave, Neutron Scattering