A rare spin effect once thought confined to bulk crystals is now confirmed in ultrathin magnetic films. This effect, known as altermagnetism, arises in a special class of antiferromagnets where electronic bands split depending on electron momentum, despite the absence of net magnetization. Unlike ferromagnets, which produce disruptive stray fields, or conventional antiferromagnets, which often conceal useful spin properties, altermagnets combine stability with robust spin-split band structures - making them attractive for spin-based devices.
A recent study by scientists from Pennsylvania State University, University of California (Santa Barbara), University of Minnesota, National Institute of Standards and Technology, Lawrence Berkeley National Laboratory, SLAC National Accelerator Laboratory, Oakridge National Laboratory and Israel's Weizmann Institute of Science demonstrated this behavior in chromium antimonide (CrSb) thin films.
Using molecular beam epitaxy, researchers synthesized epitaxial CrSb (0001) films from 10 to 100 nanometers thick on SrTiO₃ substrates, with a thin Sb₂Te₃ buffer layer to improve lattice matching. Structural analyses, including diffraction and microscopy, confirmed smooth, crystalline films with the correct NiAs-type phase and near-ideal stoichiometry.
Magnetic characterization using polarized neutron reflectometry showed no measurable net magnetization in the CrSb films, consistent with antiferromagnetic order. The crucial test came from angle-resolved photoemission spectroscopy (ARPES), which probed whether the momentum-dependent spin splitting survives at the nanoscale. Indeed, ARPES revealed bulk-like three-dimensional band structures in films as thin as 10 nanometers, with spin splitting up to 0.7 eV and g-wave directional symmetry, closely matching prior studies of bulk crystals. Remarkably, these features also persisted at room temperature.
Complementary theoretical calculations indicated that altermagnetism can remain intact down to roughly 2 nanometers, with experimental signals at 5 nanometers supporting this prediction despite increasing disorder. These results establish a practical lower bound: the essential altermagnetic band structure of CrSb is preserved at least at the 10 nanometer scale, a critical threshold for real device integration.
This work demonstrates that the defining spin-split electronic states of CrSb not only withstand nanoscale thinning but remain stable under operational conditions. By bridging the gap between bulk behavior and device-ready thin films, the study positions CrSb as a promising platform for spintronics, while also providing a roadmap for stabilizing altermagnetism in other thin-film materials.