Altermagnet Spin Current Shown for the First Time, Opening a Path to Denser Memory
Spanish-led researchers pulled hidden magnetic information out of a material with no net magnetization and read it as an electrical signal, confirming a prediction made years ago.
Physicists have shown for the first time in an experiment that an altermagnet can produce a spin current, a flow of electron spin that carries magnetic information. The result, published in the journal Nature, confirms a prediction made a few years ago by research groups in the Czech Republic and Germany. It also advances the study of a new class of magnetic materials that could support faster and denser information storage.
Altermagnets are unusual. In an ordinary ferromagnet, the magnetic moments of the atoms point the same way, and their sum creates a net magnetization. That is the magnetism used in hard disk drives, servers and magnetic stripe cards. In a conventional antiferromagnet, neighboring moments point in opposite directions and cancel, so the material keeps an internal magnetic order but shows no net magnetization. Antiferromagnets have been known for nearly a century. Altermagnets, identified only recently, also have compensated moments and no net magnetization.
The difference is inside. "This magnetic order still has two possible states, but it is indistinguishable from the outside as it does not generate a magnetic field; the information remains hidden inside the material," said Fèlix Casanova, an Ikerbasque research professor who leads the Nanodevices Group at CIC nanoGUNE. "However, in these materials, the internal magnetic order affects the behavior of electrons. This interaction enables the magnetic information to be converted into an electrical signal, thus providing a way to access it."
To prove it, the team built a nanodevice around an altermagnet made of manganese silicide, Mn5Si3. It generates a spin current in the altermagnet and carries it to a detector. Spin currents hold their information over only very short distances, so the altermagnet and detector sit just 300 nanometers apart, about one-hundredth the thickness of a human hair. When an electric current passes through the altermagnet, its internal order shapes the electrons' behavior and creates a spin current. That current travels along a metal channel and produces an electrical signal at the detector.
The researchers then checked that the signal really came from the altermagnet. Using strong magnetic fields available in their laboratory, they reversed the material's magnetic order and watched the detected signal change direction. "This correspondence confirms that the electrical signal is linked to the altermagnet's internal magnetic information and allows us to rule out the possibility that it is due to other effects in the device," said Jone Mencos, the nanoGUNE researcher who is lead author. The work is supported by an electron transport model developed by the Materials Physics Center (CFM) group, and it involved teams in the Czech Republic, Germany and France.
The appeal is practical. With no net magnetization, altermagnets can flip their magnetic order faster, are less sensitive to outside magnetic fields that can erase conventional memories, and create less interference between neighboring devices. That would allow more information to be packed into less space.
Two big problems remain. "The next challenge will be to reverse its magnetic order using low-energy electrical pulses and to make these devices function at room temperature," Casanova said. The paper is titled "Time-reversal-symmetry-breaking spin injection from a compensated magnet" (DOI: 10.1038/s41586-026-11227-7).
