Dirac-Like Ferrimagnet Ce ₃ Au ₄ Ge ₂ Bi ₄ as a Member of a Homologous Series of Square-Net Topological Materials

High Resolution Image Download MS PowerPoint Slide Square-net compounds with the HfCuSi 2 -type framework have been a promising platform for realizing topological electronic states and their interplay with quantum many-body phenomena. In these materials, the transition-metal tetrahedral layer sandwiched between square-net layers plays a crucial role in determining the correlated physical properties, yet their structural variety has been limited to the single-layer type. Here, we report the discovery of Ce 3 Au 4 Ge 2 Bi 4, a new square-net compound that represents the bilayer member of a homologous series bridging the HfCuSi 2 -type CeAuBi 2 (112 phase) and ThCr 2 Si 2 -type CeAu 2 Ge 2 (122 phase). The bilayer structure of Ce 3 Au 4 Ge 2 Bi 4 is formed by combining two tetrahedral layers of the 112 phase through the insertion of a 122-like block, resulting in two mixed-anion antifluorite-type layers. Intriguingly, both the magnetic and electronic structures are substantially modified relative to the 112 phase. Single-crystal neutron diffraction reveals that the triple Ce layers coordinated by the tetrahedral bilayer exhibit a ferrimagnetic (up–down–up) order, which can be viewed as a combination of the antiferromagnetic orders in the 112 and 122 phases. First-principles calculations demonstrate that hybridization between Ce 5 d -orbital in the spacer layer and Bi 6 p -orbital in the square-net layer reshapes the band dispersion into a type-II Dirac-like band. Consistently, magnetotransport measurements show pronounced quantum oscillations with multiple frequencies and extremely light effective masses. These results establish Ce 3 Au 4 Ge 2 Bi 4 as a prototype of a new homologous family of square-net-based topological magnets, where both magnetic order and Dirac-like band can be tuned by controlling the number of spacer layers. This tunable structural framework offers a strategy for the rational design of square-net materials with tailored functionalities.