Detection of Antiferromagnetic Orders through Heterojunction Construction and Interlayer Coupling

Two-dimensional (2D) antiferromagnets hold great promise for the application in next-generation computational devices. A critical challenge of the application of antiferromagnets lies in the detection of the N´eel vector to enable antiferromagnetic (AFM) state readout. Recently, a time-reversal-odd (T -odd) second-harmonics generation (SHG) signal has been experimentally discovered in 2D antiferromagnets. However, opposite N´eel vectors generate identical SHG intensities without phase information, hindering magnetic domain discrimination. To address this problem, we propose to use a non-magnetic substrate together with the antiferromagnet to form a heterojunction. This introduces T -even SHG that interferes with the intrinsic T -odd SHG of AFM materials, generating giant nonlinear magneto-optical (NLMO) effects that enable the detection of N´eel vector. Taking heterojunctions formed by antiferromagnetic bilayer CrBr3 and monolayer/bilayer MoS2 as examples, through symmetry analysis and first-principles calculations, we reveal the mechanism of SHG responses and derive conditions to achieve most notable NLMO effect under linearly/circularly polarized light. Theoretically, we find the strict equality between the T -even and T -odd SHG are not necessary. Practically, we discover that the T -even SHG originated from interlayer coupling interferes strongly with the T -odd SHG from 2D antiferromagnets, demonstrating exceptional advantages for generating giant NLMO effects. Our work provides a novel strategy for probing AFM order and advances the development of ultrathin magnetic storage devices.