For more than a century, physics textbooks have taught that magnets come in two fundamental types. Ferromagnets, like the bar magnets on a refrigerator, have a strong net magnetization because all their atomic spins point in the same direction. Antiferromagnets have their spins arranged in alternating opposite directions, canceling out to produce zero net magnetization.
That binary classification may need updating. A comprehensive review published July 6 in Nature Physics consolidates evidence for a third fundamental class of magnetism: altermagnetism. Unlike ferromagnets, altermagnets produce no stray magnetic fields. Unlike antiferromagnets, they can conduct strongly spin-polarized currents, potentially combining the best features of both for next-generation spintronic devices.
The Missing Magnetic Phase
The discovery that something was missing came from crystallography. Researchers noticed that certain materials, among them MnTe, RuO₂, and CrSb, exhibited a magnetic order that did not fit the conventional framework. Their spins were compensated (zero net magnetization), like antiferromagnets, but their electronic band structure showed spin splitting, which should not happen in conventional antiferromagnets where Kramers degeneracy keeps spin-up and spin-down bands paired.
The resolution came from symmetry. In conventional antiferromagnets, spin sublattices are linked by translation combined with time-reversal symmetry, a mathematical operation that flips both spin and time. In altermagnets, the sublattices are linked by a rotation combined with time-reversal symmetry. The rotation adds a directional component that lifts the spin degeneracy at general momentum points while preserving zero net magnetization.
The result is a material that combines properties previously thought mutually exclusive: spin-polarized currents in a magnet that produces no stray fields.
Why It Matters for Devices
The stray magnetic fields produced by ferromagnets are a persistent problem in miniaturized electronics. In densely packed magnetic memory arrays, the field from one bit can flip a neighboring bit, a cross-talk problem that gets worse as devices shrink. Altermagnets eliminate this problem entirely because they have no net magnetization and therefore no stray fields.
At the same time, altermagnets produce spin-polarized currents, the essential requirement for spintronic devices that use electron spin rather than charge to process and store information. They also offer intrinsically fast spin dynamics in the terahertz range, potentially enabling switching speeds far beyond what ferromagnetic devices can achieve.
The review, authored by an international team led by T. Jungwirth (Czech Academy of Sciences), J. Sinova (Johannes Gutenberg University Mainz), and L. Šmejkal (Mainz), surveys experimental milestones that have built the case for altermagnetism over the past three years: spectroscopic confirmation in MnTe (Krempaský et al., Nature, 2024), thin-film spin splitting in CrSb (Reimers et al., Nature Communications, 2024), and anomalous Hall responses in Mn₅Si₃ (Reichlova et al., Nature Communications, 2024).
What’s Been Demonstrated
The review identifies several functional phenomena already demonstrated or predicted in altermagnets:
- Giant tunneling magnetoresistance predicted in altermagnetic tunnel junctions
- Spin-splitter torque, efficient spin-orbit torque without heavy-metal layers, experimentally observed in RuO₂
- Altermagnetoelectric effect, reciprocal coupling between electric polarization and the magnetic order
- Perfect superconducting diode effect predicted in altermagnet-superconductor hybrids
- Ferroelectric-switchable altermagnetism demonstrated in multiferroic materials
- Room-temperature operation confirmed in several altermagnets, including CrSb and RuO₂
Caveats
Altermagnetism as a distinct magnetic class is still being debated in parts of the condensed matter community. Some researchers argue that it represents a subtype of antiferromagnetism rather than a genuinely new phase. The review itself acknowledges that the boundary between altermagnets and certain high-symmetry antiferromagnets is not always sharp.
Additionally, most demonstrations to date are at the material-characterization level rather than the device level. Functional spintronic devices using altermagnets, memory cells, logic gates, sensors, remain largely theoretical, though the room-temperature demonstrations bring them closer to practical reality.
Disclosure: Based on a peer-reviewed review article in Nature Physics, published July 6, 2026. DOI: 10.1038/s41567-026-03337-w. Authors: T. Jungwirth, J. Sinova, P. Wadley, D. Kriegner, H. Reichlová, F. Krizek, H. Ohno, L. Šmejkal et al.