Phenomenological description of anisotropy effects in some ferromagnetic superconductors

• Anisotropic Landau energy for description of ferromagnetic superconductors is proposed.
• Meissner phases are described with their existence and stability conditions.
• The application of the model to UGe2 is discussed.
• The limitations to apply the model for description of experimental data are explained.

We study phenomenologically the role of anisotropy in ferromagnetic superconductors UGe2, URhGe, and UCoGe for the description of their phase diagrams. We use the Ginzburg–Landau free energy in its uniform form as we will consider only spatially independent solutions. This is an expansion of previously derived results where the effect of Cooper-pair and crystal anisotropies is not taken into account. The three compounds are separately discussed with the special stress on UGe2. The main effect comes from the strong uniaxial anisotropy of magnetization while the anisotropy of Cooper pairs and crystal anisotropy only slightly change the phase diagram in the vicinity of Curie temperature. The limitations of this approach are also discussed.