Two-dimensional (2D) altermagnets have been attracting enormous research interest; however, the general guidance of global symmetry breaking poses a significant challenge of rather limited material candidates. Here, we propose a simple and widely applicable design strategy for generating both hidden and visible 2D altermagnetism in van der Waals antiferromagnetic multilayers. Based on conventional antiferromagnetic monolayers with spacetime-inversion symmetry, different types of altermagnetism can be realized, depending on interlayer magnetic interaction and local symmetry breaking. Notably, the approach has the advantage that it does not require a specific twisting/stacking order or global inversion symmetry breaking. Using a symmetry-guided framework and high-throughput computational screening, we identify diverse hidden and visible altermagnetic candidates. Beyond bilayer thicknesses, this unconventional layer-dependent nonrelativistic spin splitting mechanism exhibits a distinct odd-even effect, differing from that in conventional A-type antiferromagnets. Leveraging hidden altermagnetic order, we propose a universal multiferroic scheme for ferroelectric reversal of spin polarization. Our study greatly expands the family of 2D altermagnetic materials, circumvents stringent constraints associated with previous methods, and opens new pathways toward altermagnetic spintronics.

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• Spintronics
• Altermagnets
• Antiferromagnets
• Multiferroics
• Density functional theory
• First-principles calculations