Tuning Coupled Toroidic and Polar Orders in a Bilayer Antiferromagnet

Magnetic toroidal order features a loop-like arrangement of magnetic dipole moments, thus breaking both spatial inversion (P) and time-reversal (T) symmetries while preserving their combined PT symmetry. This PT symmetry enables a linear magnetoelectric effect, allowing the coupling between magnetic toroidicity and electric polarity. However, the detection and control of two-dimensional (2D) magnetic toroidal order and the investigation of its linear magnetoelectric response remain largely unexplored. Here, using bilayer CrSBr as a platform, which hosts an in-plane layer antiferromagnetic (AFM) order and simultaneously exhibits a magnetic toroidal order, we show compelling evidence for tuning this 2D magnetic toroidicity and its induced electric polarity through magnetic-field-dependent second harmonic generation (SHG). Under an out-of-plane magnetic field, we decompose the SHG signal into a time-reversal-odd component that scales with the magnetic toroidal moment and a time-reversal-even component that is proportional to the electric polarization. When sweeping the magnetic field from positive to negative values, we observe that the magnetic toroidicity retains its sign but diminishes in magnitude at higher fields while the electric polarity flips its sign and increases in strength at increasing fields below a critical threshold. When applying an in-plane electric field along the Néel vector direction, together with an out-of-plane field, we find that the magnetic toroidal and electric polar domains are moved in a locked fashion. These findings underscore the promise of 2D magnetic toroidal order in realizing giant linear magnetoelectric effects, opening exciting possibilities for next-generation electronic, magnetic, optical, and photonic devices enabled by 2D magnetoelectrics.