Altermagnetism: Concept, materials landscape, and future prospects

CONCEPTUAL FOUNDATIONSAltermagnetism refers to an unconventional collinear antiferromagnetic phase in which crystalline symmetry enforces momentum-dependent spin splitting despite the absence of net magnetization.The concept was theoretically consolidated by Šmejkal et al., 1 who demonstrated that such spin splitting is a symmetry-allowed and potentially widespread phenomenon rather than an exotic anomaly.In these systems, opposite spin polarizations are tied to different momenta through specific symmetry operations-typically nonsymmorphic or rotational elements-rather than through spin-orbit coupling.From a group-theoretical perspective, altermagnetism can be regarded as a subset of collinear antiferromagnetic order in which the combined timereversal and lattice-translation symmetry is broken, yielding characteristic dwave-or g-wave-like spin polarization in the Brillouin zone.This viewpoint emphasizes the physical origin of symmetry-enforced spin splitting and avoids unnecessary taxonomic debates over whether altermagnets represent a new magnetic class, as shown in Figure 1A.The essential distinction lies in their electronic signatures: momentumselective spin polarization and zero net magnetization.These features set altermagnets apart from both conventional spin-degenerate antiferromagnets and spin-orbit-driven Rashba or Weyl systems.The coexistence of spinpolarized states with compensated magnetization enables spin transport without stray fields, offering functionality naturally compatible with dense device integration.These discoveries have reshaped theoretical frameworks and inspired material searches aimed at exploiting such unconventional spin textures.