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Researchers propose a simple magnetic switch using altermagnets

Controlling magnetism in a device is not easy; unusually large magnetic fields or lots of electricity are needed, which are bulky, slow, expensive and/or waste energy. But that looks soon to change, thanks to the recent discovery of altermagnets. Now scientists are putting forth ideas for efficient switches to manage magnetism in devices.

Magnetism has traditionally come in two varieties: ferromagnetism and antiferromagnetism, based on the alignment (or not) of magnetic moments in a material. Early last year, physicists announced experimental evidence for a third variety of magnetism: altermagnetism, a different combination of spins and crystal symmetries. Researchers are now learning how to tune altermagnets, bringing science closer towards practical applications.

We're all familiar with ferromagnetism (FM), like a refrigerator magnet or compass needle, where magnetic moments in atoms lined up in parallel in a crystal. A second class was added called antiferromagnetism (AFM), where magnetic moments in a crystal align regularly in alternate directions on differing sublattices, so the crystal has no net magnetization, but usually does at low temperatures.

Altermagnets (AM) are a sort of mixture of the two: the crystalline material is ordered where the magnetic moments alternate, resulting in no net magnetization. But the spins don't simply cancel out, as in antiferromagnetism. Instead, the crystal's symmetry creates an electronic band structure with strong spins that flip in direction the deeper one probes through the material's energy bands.

Altermagnets have some properties similar to ferromagnets, but new properties as well, having no net magnetism but with strong spin-dependent effects. This makes altermagnets potentially quite useful for spintronics applications—devices where electron spin is used to carry information, akin to how electron charge carries information in electronics.

Altermagnets have been of great interest since their discovery, and new theoretical advances have shown how to create a switch for them, an important step towards applications in spintronics. The research, led by Tong Zhou of the Eastern Institute of Technology, Ningbo in China, is in Â鶹ÒùÔºical Review Letters.

"We've created a material that lets you control magnetism as easily as turning the handle on your faucet," said Zhou. "Imagine having two knobs: when they're set opposite each other, you get a special magnetic current; when they're turned the same way, it turns off. It's that simple."

Altermagnets show electronic band levels that are divided between spin-up and spin-down bands. This splitting can be used to polarize an electric current, as one spin state will flow more easily through the material than the other. This implies more rapid spintronics applications are possible that operate with greater efficiency than current spintronics devices.

What's still needed is a way to alter the spin properties of an altermagnet.

Researchers are now advocating using electric fields to do this switching. For this, electric fields have an advantage, since they're more amenable to controlling magnetic devices than are magnetic fields—easier to manipulate and implement. They would also be much faster, potentially in the sub-nanosecond range, and use less energy.

A proposal published by Zhou's group can be called an "antiferroelectric altermagnet" (AFEAM). Similarly to an antiferromagnet, an antiferroelectric (AFE) material consists of atomic structures whose electric dipoles are aligned in opposite directions.

The group hypothesized a material where the electric dipoles are coupled to magnetic spins such that the population of spin-up sublattices is linked to the spin-down sublattices through rotational symmetry. Such a material would have both antiferroelectric and altermagnetic properties.

A small applied electric field causes the electric dipoles to line up in the same direction, transforming the material into a ferroelectric (FE) crystal. In a ferroelectric state (again, dipoles aligned) it would no longer be an altermagnet but would be an antiferromagnet (magnetic moments not aligned). Then it would not polarize an electronic current. The electric field toggles the spin polarization on or off.

"Controlling magnetism means future gadgets like memory storage and computers could become much faster, use less energy, and last longer on battery power," Zhou said.

Another group and a lone researcher have also proposed technologies that also use electric fields for magnetic switching.

A group led by Qihang Liu of the Southern University of Science and Technology in Shenzhen, China, and researcher Libor Å mejkal of the Max Planck Institute for the Â鶹ÒùÔºics of Complex Systems in Germany also propose a ferroelectric switchable altermagnet, where an applied electric field interacts with deformation modes of the crystal to control the sign of the altermagnet's spin splitting.

For the deformation is the , an alternating contraction and elongation of specific bonds. For Å mejkal's the deformation comes from rotations of sublattice units within the material that, when activated electrically, reverse the ferroelectric polarization of the system, a phenomenon called the altermagnetoelectric effect.

"It's rare to bring two big ideas—antiferroelectricity and altermagnetism—together into one material and have them work in harmony. That's what makes this discovery so special," said Zhou.

"Honestly, it feels like we've uncovered a hidden switch inside materials—one that lets us toggle spin behavior without ever touching the magnetic structure. That's a game-changer."