Researchers at Tohoku University have made progress in the design of topological magnets by showing that adjusting the number of layers in a crystal can systematically influence both its magnetic and electronic properties. Their findings, published in the Journal of the American Chemical Society, build on the concept of homologous series—families of materials that share the same basic structural units but differ in the number of layers. This approach has been used for years in tuning functional oxides, such as high-temperature superconductors, but had not been applied to topological quantum materials until now. The team, led by Professor Hideaki Sakai from Tohoku University's Institute for Materials Research, focused on magnetic materials that contain square-net layers. These layers host special electrons known as topological Dirac electrons, which behave in unique ways compared to regular electrons. Between these layers, spacer layers add magnetic properties. By changing the number of these spacer layers, the researchers could alter both the electronic and magnetic characteristics of the material. They created a new compound, Ce₃Au₄Ge₂Bi₄, which contains two spacer layers between its square-net layers. This compound connects a known single-layer material, CeAuBi₂, with an infinite-layer material, CeAu₂Ge₂, forming a new homologous series based on the same structural building blocks. Neutron scattering experiments revealed that the number of layers significantly affects the magnetic order of the material. The single-layer compound exhibits antiferromagnetism, where magnetic moments cancel each other out. In contrast, Ce₃Au₄Ge₂Bi₄ shows ferrimagnetism, where opposing magnetic moments do not fully cancel, leading to a net magnetization. The researchers also studied how the electronic structure changes across the series. Their theoretical models and high-magnetic-field measurements showed that the Dirac electrons in Ce₃Au₄Ge₂Bi₄ form a highly tilted type-II Dirac cone, a rare electronic configuration that differs from what would be expected in a vacuum. “This approach allows us to systematically tune both magnetic and topological properties by varying the number of layers, rather than searching for new materials one by one,” said Sakai. The study demonstrates that homologous-series design can be extended to topological quantum materials. By combining layer-number control with changes in the chemical elements used, researchers could create a wide range of materials with unique combinations of magnetic and topological properties. These materials may have applications in emerging fields such as spintronics and quantum technologies, which rely on the manipulation of electron spin and quantum states. The team plans to further investigate the transport properties of the highly tilted type-II Dirac bands and explore how they interact with the material’s spontaneous magnetization. They will also use spectroscopic techniques to study the material’s microscopic electronic structure. Using the homologous-series framework, the researchers aim to synthesize new compounds with different crystal structures, potentially uncovering novel combinations of topological and magnetic states.