Visualization of Electrically Controllable Magnetic Domains in a Quasi-One-Dimensional Quantum Antiferromagnet BaCu2Si2O7
PI of Joint-use project: Kenta Kimura
Host lab: Masuda Group
Host lab: Masuda Group
Quasi-one-dimensional quantum antiferromagnets (q1D-QAFMs) consist of chains of magnetic ions with a small spin quantum number (S = 1/2 and 1), where the antiferromagnetic interactions within the chains are much stronger than the interchain interactions. q1D-QAFMs have attracted attention for their potential to exhibit exotic phenomena (e.g., spin liquid behavior and topological spin excitations) and their possible application in quantum spintronic technology. Like other types of antiferromagnets, q1D-QAFMs will form a pair of domain states when undergoing an antiferromagnetic transition due to interchain interactions, typically represented by an “up-down-up-down” state and a “down-up-down-up” state. These domains are randomly distributed in a single crystal sample, and their observation and manipulation are critical for device applications. However, observing domain patterns in q1D-QAFMs appears to be challenging, not only because of the absence of net magnetization, but also because of strong quantum fluctuations that significantly reduce the ordered components of individual spins. Indeed, there has been no experimental observation of the domain pattern in q1D-QAFMs.
In the present study [1], we successfully visualize antiferromagnetic domains in one of the most representative spin-1/2 q1D-QAFMs, BaCu2Si2O7, which exhibits an antiferromagnetic order below TN =

Figure 1(b) shows the optical microscopy image of a thin plate sample taken at
On a qualitative level, the observed DW anisotropy can be explained in terms of the anisotropy of the magnetic interactions. Figure 1(d) shows schematic spin arrangements near the DW parallel and perpendicular to the spin chains, denoted by DW|| and DW⊥, respectively. The formation of DW⊥ costs the energy governed by the strong intrachain interaction, which is 2 orders of magnitude larger than the interchain interactions governing DW||. This suggests that DW|| is preferable, in agreement with the experimental observation. However, we find that the anisotropy of the magnetic interactions is much larger than the anisotropy of the DWs, which is estimated as the ratio of the lengths of DW|| (LDW||) and DW⊥ (LDW⊥): LDW||/ LDW⊥ ~ 10. This implies that another factor should also be considered to understand the DW formation. To our knowledge, there is no relevant theory available. Future work is needed to understand the microscopic origin of the DW anisotropy in the q1D-QAFMs.
In conclusion, the present study will contribute to the understanding of the domain physics of q1D-QAFMs. It also raises an interesting question as to whether the domain pattern observed in BaCu2Si2O7 is a material specific property or intrinsic to q1D-QAFMs.
References
- [1] M. Moromizato T. Miyake, T. Masuda, T. Kimura, and K. Kimura, Phys. Rev. Lett. 133, 086701 (2024).
- [2] M. Kenzelmann, A. Zheludev, S. Raymond, E. Ressouche, T. Masuda, P. Böni, K. Kakurai, I. Tsukada, K. Uchinokura, and R. Coldea, Phys. Rev. B 64, 054422 (2001).
- [3] K. Kimura and T. Kimura, APL Mater. 11, 100902 (2023).