In the wild world of magnets, there are two familiar moods. One is the loud, defiant chorus of aligned spins that march in step, producing a clear net magnetization you can feel with a compass. The other is a careful counterbalance: neighboring spins point in opposite directions so their magnetic moments cancel out. That second mood—antiferromagnetism—has long been treated as the quiet, unassuming sibling of ferromagnetism. Yet a new line of thinking is teaching us that quiet can still be full of surprises. A study led by researchers at the National Institute for Materials Science (NIMS) in Japan’s MANA center, with collaborators from The University of Osaka, argues that antiferromagnets can host a rare, almost paradoxical mix: time-reversal symmetry can be broken and yet the electron bands can stay spin-degenerate, and still give rise to effects we usually associate with ferromagnets. This is altermagnetism, a word that sounds like a hinge between familiar magnetism and something genuinely new.
The paper, led by I. V. Solovyev with S. A. Nikolaev and A. Tanaka, builds a bridge between three phenomena that have long lived on their own in different corners of condensed matter physics: weak ferromagnetism (WF), the anomalous Hall effect (AHE), and net orbital magnetization (OM). Using a realistic model relevant to La2CuO4 and related perovskites, the team shows that all three can be traced back to the way electrons hop between atoms and how spin-orbit coupling twists those hops. The key twist is that some DM interactions flip sign across bonds, while others keep the sign the same. That subtle distinction matters a lot for what the electrons do near the Fermi surface.
To a broad audience, the message is both practical and poetic: the same ingredient—how the lattice distorts and how spins feel the lattice—can shape a world where time-reversal symmetry feels broken, yet the spin symmetry remains stubbornly intact in the band structure. It’s a reminder that symmetry, not just magnetization, can govern what electrons do when they deflect to the side, or when they align their orbital motion with a subtle twist of the lattice. And it’s a reminder that the “orbit” of electrons—their orbital motion around atoms—can be as central as the spin itself in determining a material’s magnetic and transport personality.
