Altermagnets: The Hidden Dance of Spins express
Altermagnets resemble a ballroom where couples spin in opposite directions: the hall itself is still, but inside, ordered motion seethes. Similarly, electron spins (the direction of their rotation) in these materials form intricate patterns without creating an overall magnetism. This hidden "choreography" allows electrons with different spins to move in opposite directions, like dancers spreading out to the edges of the floor. This effect separates charge carriers without an external magnet.
Physicists have proposed a theoretical description for achiral altermagnets, where spins not only point up or down but twist into three-dimensional figures that are symmetric under reflection. The model, rooted in the work of Lev Landau and relying on conventional particle physics, predicts an enhancement of spin current and piezomagnetism — the ability to slightly magnetize when compressed, as if pressing on the dance floor causes some couples to move in sync.
An experiment with NiS2 crystal showed that upon cooling, internal disorder decreases and spins align into two successive structures. Light-based analysis confirmed that the unconventional geometry makes the order remarkably robust — tougher than in simple altermagnets. This opens the way to spintronic devices, where information is carried by spin direction, promising faster and more energy-efficient electronics.
Original abstract
as written by the authors arXiv:2603.01329
Altermagnets (A$$\ell$$Ms) constitute a novel family of magnetic materials characterized by the absence of net magnetization and the presence of spin-polarized band structures. Whereas A$$\ell$$M phases were initially proposed in collinear structures, the recently discovered noncollinear chiral A$$\ell$$Ms stand out for their distinct hedgehog spin texture and multifunctionality in spintronics. In this work, we deepen the characterization of these systems by constructing a Landau theory for noncollinear achiral A$$\ell$$Ms. Furthermore, we demonstrate that the achiral symmetry of the crystal is reflected in the spin texture in reciprocal space, which presents only spatial-even multipoles. These multipoles, distinguished from those in collinear A$$\ell$$Ms via the high-order secondary order parameters, can couple to many phenomena such as the spin Hall effect and piezomagnetic effect. To exemplify our theory, we study the noncollinear achiral magnet NiS$$_2$$ within the framework of altermagnetism, showcasing both spin Hall and piezomagnetic effects in a prototypical correlated Mott insulator that provides an ideal platform to explore the interplay between strong electronic correlations, crystal symmetry, and altermagnetic spin textures. Interestingly, altermagnetism emerges in two magnetic ordered phases of NiS$$_2$$ upon lowering the temperature. The non-collinearity strengthens the robustness of A$$\ell$$M order, as the anti-ferromagnetism induced by the strong correlations will not impose effective time-reversal symmetry as in the collinear case. Our results suggest non-collinear achiral A$$\ell$$Ms as a promising platform for spintronics applications due to the potential to achieve various spin textures with different magnetic orders.
Altermagnetism was theoretically predicted only in 2019, but over a hundred materials with such properties have already been found, including NiS2.
Controlling spins without magnetic fields transports us to a sci-fi world where 'spin computers' operate without energy consumption, like in novels about the far future.