Magnetic structures in the coexistence phase of superconductivity and weak ferromagnetism

The phases of superconductivity and weak ferromagnetism coexistence are considered. The following situations may realize below the Neel temperature depending on the weak ferromagnetic moment value: the phase with the domain-like magnetic structure when the vectors of anti-ferromagnetism 1 and weak ferromagnetism m have opposite directions in the neighbouring domains, Meissner ferromagnetic phase (1, and m are constant) which has no analogy in other magnetic superconductors and self-induced vertex phase (the directions of 1 and m are constant and their values vary smoothly in space). The new tetragonal body centered phase of ErRH₄B₄ may prove to be the first weak ferromagnetic superconductor.