Unified Theory of Atomic-Group-Based Magnetism in Carbon Allotropes

Traditional carbon allotropes, such as graphene, diamond,
nanotubes,
and fullerenes, are typically nonmagnetic. However, recent experimental
observations of intrinsic magnetism challenge conventional theories.
The microscopic origin, exchange interactions, and design strategies
for magnetic carbon structures, particularly three-dimensional (3D)
allotropes, remain elusive. Here, combining first-principles calculations
with hybrid orbital analysis, we establish a unified framework showing
that magnetism arises from symmetry breaking of unhybridized 2p orbitals within atomic groups exhibiting bent sp-sp2 or trigonal pyramidal sp2-sp3 hybridizations.
Distinct from conventional atomic-centered magnetism theories, our
atomic-group-based paradigm systematically predicts magnetic carbon
allotropes from zero-dimensional to 3D systems. We further propose
a general design strategy and predict a family of metastable two-dimensional
and 3D phases displaying intrinsic itinerant ferromagnetism or antiferromagnetism.
These findings lay the groundwork for a p-block magnetism
theory and open avenues for spintronic and quantum material design.