Spin-Polarized Antiferromagnets for Spintronics.

Spin-polarized antiferromagnets (AFMs), including altermagnets, noncollinear AFMs, and 2D layer-polarized AFMs, have emerged as transformative materials for next-generation spintronic and optoelectronic technologies. These systems uniquely combine spin-polarized electronic states with vanishing net magnetization, enabling ultrafast spin dynamics, high-density integration, and robustness against stray magnetic fields. Their unconventional symmetry-breaking mechanisms-governed by crystal symmetry, chiral spin textures, or interlayer potential control-give rise to emergent phenomena previously exclusive to ferromagnets: nonrelativistic spin-momentum locking, spontaneous anomalous transport phenomena, gate-tunable magneto-optical responses, nonrelativistic spin-polarized current, and tunneling magnetoresistance effect. This review systematically examines the fundamental principles linking symmetry, band topology, and transport properties across these material classes, synthesizing recent breakthroughs in both theory and experiment. Critical challenges are further identified in achieving room-temperature functionality, scalable Néel vector control, and coherent spin-current manipulation, while outlining pathways to harness these materials for ultra-low-power memory, spin-logic architectures, and quantum information technologies.