Designing Spin Symmetry for Altermagnetism with Strong Magnetoelectric Coupling.

Altermagnets, a recently identified class of collinear magnets, exhibit unique properties such as zero net magnetization and spin polarization dictated by lattice symmetry, making them a subject of intense research. In contrast to conventional strategies for inducing altermagnetism in antiferromagnets that rely on manipulating real-space symmetry, this work introduces a novel and general approach to achieving altermagnetism by modulating spin-space symmetry. Through a combination of tight-binding models and first-principles calculations, the microscopic origin of altermagnetism driven by spin-space symmetry is uncovered, and the mechanism underlying enhanced spin splitting is identified. Furthermore, it is demonstrated that this spin-space modulation can synergistically interact with ferroelectricity, enabling a spin symmetry-dependent magnetoelectric coupling mechanism that is distinct from conventional multiferroics. This unique coupling is validated by the magneto-optical Kerr effect, providing a robust theoretical foundation for the development of next-generation spintronic devices that harness the potential of altermagnetism.