Researchers electrically read the hidden magnetic information of altermagnets — a new class of materials

Altermagnets are a new class of magnetic materials. In conventional magnets, or ferromagnets, the magnetic moments of the atoms point in the same direction. The sum of these moments creates a net magnetisation, which is responsible for the magnetic field we usually associate with a magnet, but which is also used as information in the magnetic memories we use daily in devices such as hard disk drives, servers and magnetic stripe cards. In conventional antiferromagnets, however, the magnetic moments point in opposing directions and cancel each other out, so the material does not exhibit net magnetisation, though it does maintain an internal magnetic order.

Although antiferromagnets have been known for almost a century, it was only recently that a new class of materials with compensated magnetic moments was identified: the altermagnets. As with antiferromagnets, altermagnets do not exhibit net magnetisation. “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. However, in these materials, the internal magnetic order affects the behaviour of electrons. This interaction enables the magnetic information to be converted into an electrical signal, thus providing a way to access it”, points out Fèlix Casanova, Ikerbasque Research Professor and leader of the Nanodevices Group at CIC nanoGUNE.

To demonstrate it, the research team developed a nanodevice that can extract the magnetic information from the altermagnet and transport it to a detector. CIC nanoGUNE’s experience in manufacturing nanoscale devices has been key to this advance, since the spin currents —which transport information associated with the spin orientation of the electrons— retain this information only over very short distances. “In the device developed, the altermagnet and detector are separated by just 300 nanometres, approximately one-hundredth the thickness of a human hair. By passing an electric current through the altermagnet, its internal magnetic order affects the behaviour of the electrons and generates a spin current that propagates through a metal conduit until it reaches the detector, where it produces an electrical signal”, explains Jone Mencos, researcher with the Nanodevices Group at CIC nanoGUNE and lead author of the work. Next, “the team reversed the magnetic order of the material using strong magnetic fields, available in our laboratory, and observed that the detected signal also changes 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 of being due to other effects in the device”, adds the CIC nanoGUNE researcher.

According to the research team, altermagnets could pave the way to faster, denser and more robust magnetic memories. Since there is no net magnetisation, these materials can reverse their magnetic order more quickly, they are less sensitive to external magnetic fields that can erase conventional magnetic memories, and they generate fewer interferences between devices, which would allow more information to be stored in less space. “The next challenge will be to reverse its magnetic order using low-energy electrical pulses and to make these devices function at room temperature”, says Fèlix Casanova.