Magnetism and superconductivity in the layered hexagonal transition metal pnictides

We investigate the electronic and magnetic structures of the 122(AM2B2) hexagonal transition metal pnictides with A=(Sr,Ca),M=(Cr,Mn,Fe,Co,Ni), and B=(As,P,Sb). It is found that the family of materials shares critical similarities with those of tetragonal structures that include the famous iron-based higherature superconductors. In both families, the next-nearest-neighbor (NNN) effective antiferromagnetic (AFM) exchange couplings reach the maximum value in the iron-based materials. While the NNN couplings in the latter are known to be responsible for the C-type AFM state and to result in the extended s-wave superconducting state upon doping, they cause the former to be extremely frustrated magnetic systems and can lead to a time-reversal symmetry-broken d+id superconducting state upon doping. Thus, if synthesized, iron-based compounds with hexagonal structure can help us to determine the origin of higherature superconductivity.