Effect of the Temperature and Concentration of Magnetic Atoms on Phase Diagrams and Order Parameters in Ferromagnetic Superconductors

Abstract

AbstractUsing the free energy functional with two coupled order parameters the model of a rare earth ferromagnetic superconductor is considered by means of the Landau theory of phase transitions. By making the experimentally verified assumption about the dependence of critical temperatures for magnetic and superconducting subsystems on the concentration of magnetic rare earth atoms, the resulting phase diagrams are analysed in the temperature—concentration plane. It turns out that for weak coupling between magnetic and superconducting subsystems the uniform coexistence state of ferromagnetism and superconductivity sets in, while for strong coupling a spatially non‐uniform metastable state exhibiting hysteretic behaviour for ferromagnetic and superconducting phase appears. The explicit dependence of the order parameters on the temperature and concentration of magnetic atoms is also given.