AM-C33: an altermagnetic carbon

Altermagnetic materials have recently garnered significant attention due to their combined advantages of spin-splitting characteristics inherent to ferromagnets and the zero-net-moment stability of antiferromagnets. p-electron spintronic materials intrinsically exhibit long-distance spin coherence and long spin lifetimes. However, to date, no theoretical or experimental realization of three-dimensional p-electron altermagnets has been reported. Herein, using first-principles calculations, we proposed a fully carbon-based p-electron altermagnetic semiconductor, denoted as AM-C33, featuring a bandgap of 0.52 eV, spin-splitting energy of 0.31 eV, and transition temperature of 121.5 K. The altermagnetic behavior arises from the tetrahedrally distributed spin atoms, in which the opposite-spin sublattices are connected by a four-fold inversion axis. In addition, strain engineering enables tuning of both the bandgap and spin-splitting magnitudes while preserving its altermagnetic order. Furthermore, this material hosts metastable phases exhibiting distinct functionalities, including a half-metal ferromagnetic state and a bipolar magnetic semiconductor ferrimagnetic state. Hence, the present work presents great promise for designing p-electron altermagnets, particularly advancing carbon-based altermagnetic materials for spintronic applications.