Ferromagnetism and reentrant superconductivity

We consider the extended two-band s-f model with additional terms, describing intersite Cooper pairs interaction between 4f (5f) and conduction electrons. Numerical calculations show that for a proper choice of model parameters the system possesses three critical temperatures: T-c (Curie temperature), T-s, and T-s2 (lower and upper transition temperatures to the superconducting state). The critical temperatures fulfil the relation T-s1 < T-c < T-s2. The system is ferromagnetic and normal for T < T-s1, ferromagnetic and superconducting for T-s1 < T < T-c, paramagnetic and superconducting for T-c < T < T-s2, paramagnetic and normal for T > T-s2, as well. The calculations of the Curie temperature T-c and upper critical temperature T-s2 as functions of the model parameters (3D plots) show the appearance of the reentrant superconductivity when T-s2 > T-c. The calculated temperature dependence of the DC resistivity (3D plots) is in many cases similar to the typical reentrant behaviour, experimentally found for magnetic superconductors (e.g. ErRh4B4, HoMo6S8), (C) 1998 Elsevier Science B.V. All rights reserved.