Quasiclassical Theory of C₄-Symmetric Magnetic Order in Disordered Multiband Metals

Recent experimental studies performed in the normal state of iron-based superconductors have discovered the existence of the C₄-symmetric (tetragonal) itinerant magnetic state. This state can be described as a spin density wave with two distinct magnetic vectors (Formula presented.) and (Formula presented.). Given an itinerant nature of magnetism in iron-pnictides, we develop a quasiclassical theory of tetragonal magnetic order in disordered three-band metal with anisotropic band structure. Within our model we find that the C₄-symmetric magnetism competes with the C₂-symmetric state with a single (Formula presented.) magnetic structure vector. Our main results is that disorder promotes tetragonal magnetic state which is in agreement with earlier theoretical studies.