Co1/4TaSe2 shows altermagnetism, a new magnetic state

Researchers at the University of Central Florida report experimental evidence of a new form of magnetism in the layered material Co1/4TaSe2. The discovery, described by ScienceDaily, could help advance spintronics — electronics that use the spin of electrons rather than their charge.

The team, led by physics professor Madhab Neupane, identified altermagnetism, a magnetic state that was recognized only recently. Altermagnets combine properties of two better-known types: ferromagnets, which produce an overall magnetic field but generate stray fields that interfere with nearby components, and antiferromagnets, whose magnetic moments cancel each other but lack some electronic features useful for technology.

Detecting the effect

To confirm that Co1/4TaSe2 displayed altermagnetism, the researchers used angle-resolved photoemission spectroscopy (ARPES) to measure electron behavior. They first observed a distinct splitting in the material's electronic bands, then used spin-resolved ARPES to show that the separated states had opposite spin polarizations — a key signature of altermagnetism.

“The significance became clear once the experimental measurements consistently matched our theoretical predictions,” Neupane says. “Seeing those independent pieces of evidence converge gave us confidence that we had identified a genuine layered altermagnet.”

Why the material matters

Co1/4TaSe2 belongs to a class of materials called transition-metal dichalcogenides (TMDs), whose extremely thin layers are weakly connected. Scientists can separate and restack those layers into very thin structures, making the material easy to modify for thin-film devices.

Magnetic cobalt atoms positioned between the layers give the material its unusual magnetic character. Because altermagnets generate and detect spin currents without producing stray magnetic fields, they are attractive for spintronics, ultrafast memory, terahertz networks, and energy-efficient electronics.

“These materials are distinguished from more conventional antiferromagnets by their ability to generate and detect spin currents without the negative effect of producing stray fields,” Neupane says.

Open questions

Researchers still do not fully understand why altermagnetism forms in this material, how it competes with ferromagnetism and antiferromagnetism, or exactly how it behaves under different conditions. Theoretical work suggests competing interactions among electrons may influence the magnetic order, but those ideas need experimental verification.

The layered structure offers a flexible platform to investigate those questions. “Now that we have identified several platforms for answering these questions, more advanced studies into these materials are underway,” Neupane says.

The work was supported by the U.S. Department of Energy.

• altermagnetism
• Co1/4TaSe2
• Madhab Neupane
• spintronics
• transition-metal dichalcogenides
• UCF