Why in news?
Materials scientists in Japan and Europe have confirmed that the compound ruthenium dioxide (RuO₂) exhibits a newly discovered form of magnetism known as altermagnetism. By fabricating single‑crystal thin films and measuring their electronic properties, the researchers observed a spin‑splitting effect without an overall magnetic field. This finding paves the way for faster, more energy‑efficient memory and computing devices.
Background
Traditional magnets are classified as ferromagnets, in which atomic spins align in the same direction creating a net magnetic field, or antiferromagnets, where neighbouring spins point in opposite directions canceling out the external field. Altermagnets form a third class: their crystal structure arranges spins in alternating patterns so that the net field is zero, yet the magnetic moments are oriented in ways that allow electrons of opposite spins to travel differently. This subtle symmetry results in spin‑polarised currents even without an applied magnetic field.
What researchers did
- Thin‑film fabrication: The team grew epitaxial RuO₂ films on sapphire substrates such that the crystals were oriented in a single direction. This avoided averaging out the spin effects that occur in polycrystalline samples.
- X‑ray magnetic linear dichroism: They shone polarised X‑rays onto the films and measured how the absorption depended on the orientation of electron spins, revealing the presence of alternating magnetic moments.
- Spin‑split magnetoresistance: Electrical measurements showed that the resistance of the film depended on the spin orientation of electrons, confirming that RuO₂ conducts spin‑polarised currents despite having no net magnetisation.
- Agreement with theory: The results matched predictions from quantum mechanical calculations, strengthening the case for RuO₂ as an altermagnet.
Significance
- New platform for spintronics: Devices that manipulate electron spin rather than charge – such as spin‑transfer torque memory – can operate faster and consume less power. Altermagnets offer spin‑polarised currents without stray magnetic fields, simplifying device architectures.
- Robustness: Unlike ferromagnets, altermagnets are insensitive to external magnetic disturbances and can operate at high frequencies without cross‑talk. This could lead to denser, more stable data storage.
- Expanding the magnetic family: The discovery of altermagnetism broadens our understanding of how electron spins can order in solids. It may inspire the search for other compounds with similar properties, including room‑temperature altermagnets.
Conclusion
Identifying RuO₂ as an altermagnet marks an important advance in condensed‑matter physics. By harnessing the unique spin‑splitting behaviour of altermagnets, engineers may design electronic components that are faster, more compact and less susceptible to interference than current technologies. Ongoing research will explore how to integrate such materials into practical devices.
Source: Phys.org
