Researchers at the University of Central Florida and collaborating institutions have found experimental evidence of altermagnetism in a layered material called Co₁/₄TaSe₂. The discovery, published in Nature Communications, combines characteristics of ferromagnetism and antiferromagnetism, offering a versatile platform for future spintronics and energy-efficient electronic devices.
For decades, standard physics recognized two primary magnetic states: ferromagnetism, which forms classic north-and-south-pole setups like fridge magnets, and antiferromagnetism, where microscopic magnetic moments point in opposing directions and cancel each other out.
Ferromagnets generate strong fields useful for data storage, but their stray magnetic fields can interfere with nearby electronic components and computer chips. Traditional antiferromagnetism squashes the stray fields because their moments compensate, but their internal states remain difficult to control and detect while eliminating attractive properties that may make a material useful. Now, an emerging third route through magnetism known as altermagnetism bridges those two extremes.
Detecting Altermagnetism in Co₁/₄TaSe₂
Scientists led by University of Central Florida Professor of Physics Madhab Neupane have identified signatures of this unusual magnetic state in Co₁/₄TaSe₂, a layered compound made from cobalt, tantalum, and selenium.
To produce usable crystals, researchers baked the constituent elements at more than 900 degrees Celsius, or 1,700 degrees Fahrenheit, across two weeks. Measurements were conducted well below the material’s magnetic transition temperature of 178 kelvins. At these low temperatures, cobalt moments form an ordered arrangement where spins align within individual layers but point oppositely between neighboring layers.
“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,”
Madhab Neupane, Professor of Physics at the University of Central Florida
Measuring Momentum-Dependent Spin Splitting
To investigate how electrons behave inside the crystal, the research team relied on angle-resolved photoemission spectroscopy, commonly known as ARPES. The technique hits a material with a beam of light, causing it to eject an electron so scientists can determine its energy and its direction, allowing them to reconstruct an energetic band structure mapping where electrons can and cannot exist.
Initial ARPES scans revealed a characteristic splitting of electronic energy bands that closely matched calculations based on density functional theory. The team then applied spin-resolved ARPES to verify whether those separated bands carried distinct spin polarizations, referring to how an elementary particle’s spin is aligned to a certain direction with particles spinning up or down. Across a prominent electronic feature, the measured spin polarization shifted from approximately negative 13% to positive 13%.
Measurements for the project were conducted at national synchrotron facilities, including the Advanced Light Source at Lawrence Berkeley National Laboratory and the Stanford Synchrotron Radiation Lightsource. Neupane’s laboratory at the University of Central Florida also houses molecular beam epitaxy, ARPES, and time-resolved ARPES systems.
Developing Ultrafast Memory
The discovery establishes Co₁/₄TaSe₂ as an adaptable platform for exploring quantum mechanical properties that could alter how information travels through a circuit. Because the compound belongs to a family of layered materials that can be thinned and combined into heterostructures, it offers an unusually flexible medium for study, with doctoral candidates Milo Sprague, Arun K. Kumay, and Mazharul Islam Mondal contributing alongside Professor Neupane in research credited visually to Antoine Hart.
Researchers note that practical devices remain a longer-term goal, but the verified presence of momentum-dependent spin splitting provides a foundation. As theoretical debates continue regarding how spin-polarized electronic states interact with other magnetic phenomena, scientists now possess a tunable material positioned for use in spintronics, ultrafast memory devices, terahertz networks, and energy-efficient electronics to explore these questions in the laboratory.
