Direct observation of tunable magnetic domains in noncentrosymmetric ferromagnetic Weyl semimetal

Textures and dynamics of magnetic domain walls (DW) in Weyl semimetals are predicted to have their electromagnetic behavior strongly altered by emergent gauge fields. Therefore, knowing the detailed domain physics in these materials is important for the experimental realization of such theoretical proposals. In this work, we imaged the spontaneous magnetization and magnetic susceptibility of a ferromagnetic (FM) Weyl semimetal: CeAlSi [1,2]. We utilized a scanning SQUID susceptometer microscopy, which can be considered a type of low-frequency and low-energy spectroscopic imaging technique [3,4]. We observed large ferromagnetic DWs lined-up with the main crystallographic directions and discovered the coexistence of stable and metastable domain phases, which likely arise due to the magnetoelastic and magnetostriction effects and are potentially highly tunable with small strains. We found that the pattern of the FM domains is strongly correlated with both the amplitude and the orientation of an external in-plane magnetic field. The average area of the stable domains increases strongly even with very small fields. The length of the domain walls is maximized when the in-plane field is directed along the main crystallographic axes and the area of the domains is maximized when the field is at 45o to the crystallographic axes. Our results show how these domains and heterogeneous phases can be fine-tuned and, therefore, this work provides guidance for future studies on the fundamental interplay between magnetism and electronic properties in Weyl systems and how to utilize these systems in realizing new devices.

[1] H.-Y. Yang et al., ArXiv:2006.07943 to appear in Phys. Rev. B (2021).
[2] B. Xu et al., Adv. Quantum Technol., Cover Article, 2000101 (2021).
[3] Z.-C. Wang et al., Advanced Materials, 2005755 (2021).
[4] C. Herrera et al., Phys. Rev. B, Editor's Choice Article, 103, 024528 (2021).