  We investigate magnetism in amorphous carbon as suggested by the recently
reported ferromagnetism in a new form of amorphous carbon. We use spin
constrained first-principles simulations to obtain amorphous carbon structures
with the desired magnetization. We show that the existence of $sp^2$-like
3-fold coordinated carbon atoms plays an important role in obtaining magnetism
in amorphous carbon. The detailed geometries of 3-fold carbon atoms induce the
magnetic order in amorphous carbon.
