Reduced iron ordered moment and negative TC-pressure coefficient in iron-arsenide superconductors

Abstract

The striped antiferromagnetic phase of iron-arsenides is investigated by the density functional calculations including Coulomb repulsion. Two low moment solutions with m ≈ 0.4 μB and m ≈ 1.0 μB have been found from calculations. The electronic structures indicate that the low moment states originate in the strong orbital hybridization between antiferromagnetic Fe neighbors. Therefore, the geometry of FeAs4 tetrahedron, which is characterized by a parameter of hAs/a, is crucial to the low moment states. We show that the puzzling negative TC-pressure coefficient of iron-arsenides can be consistently explained by the obtained low moment states.