Altermagnetism Emerges in Graphite, Enabling Novel Spintronic Device Potential.

Vanadium-intercalated graphite exhibits alternamagnetism, a magnetic phase characterised by momentum-dependent spin splitting and zero net magnetisation. First-principles calculations reveal a 270 meV spin splitting, robust against spin-orbit coupling, with a predicted magnetic transition temperature of 228 K, suggesting potential for spintronic devices.

The pursuit of materials exhibiting novel magnetic properties continues to drive innovation in spintronics and materials science. Recent research focuses on identifying systems that move beyond conventional magnetism, exploring phases where spin polarisation arises not from a net magnetic moment, but from momentum-dependent spin textures. A collaborative team, comprising Weida Fu, Guo-Dong Zhao, Tao Hu, Wencai Yi, Hui Zhang, Alessandro Stroppa, Wei Ren, and Zhongming Ren, reports the prediction of such a phase, termed altermagnetism, within vanadium-intercalated graphite compounds. Their work, detailed in the article ‘First-principles prediction of altermagnetism in transition metal graphite intercalation compounds’, utilises computational modelling to demonstrate that these materials exhibit inherent altermagnetic behaviour, offering potential for applications in zero-field spin-polarised current generation and topologically robust spin transport. Graphite intercalation compounds (GICs) are materials formed by inserting atoms, ions, or molecules between the layers of graphite, altering its electronic and structural characteristics. Altermagnetism, a relatively recently identified magnetic phase, is characterised by compensated spin ordering, meaning the net magnetisation is zero, coupled with spin splitting that varies depending on the electron’s momentum.

Vanadium-intercalated graphite compounds demonstrate altermagnetism, a magnetic phase characterised by compensated spin ordering and momentum-dependent spin splitting. These compounds arise within graphite intercalation compounds (GICs), materials extensively studied for their adjustable electronic and structural characteristics, and present a new route for spintronic applications. First-principles calculations corroborate the inherent altermagnetic properties, originating from their hexagonal crystal system and antiferromagnetic arrangement of vanadium atoms. This configuration enforces alternating spin polarisation in momentum space, crucially maintaining zero net magnetisation, a vital feature for advanced spintronic devices.

Calculations reveal a substantial spin splitting of approximately 270 milli-electronvolts (meV) along high-symmetry directions, directly confirming the altermagnetic signature and providing a quantifiable measure of the effect. Spin splitting refers to the divergence of energy levels for electrons with different spin orientations in a material, a key phenomenon exploited in spintronics. The research demonstrates minimal sensitivity of this spin splitting to spin-orbit coupling (SOC), indicating that exchange interactions, arising from the quantum mechanical exchange force between electrons, dominate relativistic effects and ensuring the robustness of the altermagnetic state. Spin-orbit coupling is a relativistic effect that arises from the interaction between an electron’s spin and its orbital motion.

Monte Carlo simulations predict a magnetic transition temperature ($T_c$) of approximately 228 Kelvin, suggesting stable magnetic ordering is achievable above liquid nitrogen temperatures and broadening the scope of potential applications. This relatively high transition temperature enhances the practical viability of these materials for technological implementation, reducing the need for complex cooling systems. The combination of symmetry-protected spin textures, minimal spin-orbit coupling dependence, and elevated operating temperature positions vanadium-intercalated graphite compounds as promising candidates for spintronic devices.

Specifically, these materials offer potential for zero-field spin-polarized current generation, eliminating the need for external magnetic fields and reducing energy consumption in electronic devices. Spin-polarized current refers to an electrical current where the majority of charge carriers have the same spin orientation. Furthermore, the unique spin textures offer the possibility of topologically robust spin transport, leading to more reliable and efficient devices. Topologically robust spin transport refers to the ability of spin information to be carried through a material without being scattered or lost, due to the material’s topological properties. This work represents a significant advancement in materials science, opening up new avenues for developing novel spintronic materials with tailored magnetic properties and enhanced device performance. The findings pave the way for the development of next-generation spintronic devices with improved energy efficiency and performance.