Realization of high-temperature metallic altermagnetism in transition metal graphite intercalation compounds

Abstract

We report the emergence of altermagnetism, a magnetic phase characterized by the coexistence of compensated spin ordering and momentum-dependent spin splitting, in graphite intercalation compounds (GICs), a prototypical material system long investigated for its tunable electronic and structural properties. Through first-principles calculations, we demonstrate that vanadium-intercalated stage-1 graphite compounds (C₁₆V₂) exhibit inherent altermagnetic properties. The interplay between structural symmetry and the antiferromagnetic ordering of the V sublattice is described by specific spin groups that enforce alternating spin polarization in momentum space while maintaining zero net magnetization. The altermagnetism is robustly sustained throughout this stoichiometric framework, while the spin-splitting pattern undergoes a symmetry-driven evolution from g-wave (~272 meV) in the high-symmetry hexagonal phase to d-wave (~201 meV) in the orthorhombic phase. Crucially, the spin splitting exhibits minimal sensitivity to spin-orbit coupling effects, highlighting the dominance of exchange interactions over relativistic effects. Monte Carlo simulations predict magnetic transition temperatures of ~680 K and ~880 K for stable phases. These well-above-room-temperature values identify the material as a viable candidate for pratical altermagnetic applications. As the first demonstration of a metallic carbon-hosted altermagnet, our work establishes a promising platform for developing next-generation electronic materials functional at room temperature.