We study the order-parameter symmetry in a hexagonal crystal with coexisting superconductivity and ferromagnetism. An experimental example is provided by carbon-based materials, such as graphite-sulfur composites, in which an evidence of such coexistence has been recently discovered. The presence of a nonzero magnetization in the normal phase brings about considerable changes in the symmetry classification of superconducting states compared to the nonmagnetic case.

• Received 20 August 2002

DOI:https://doi.org/10.1103/PhysRevB.66.212509