Phenomenological theory of superconductivity and magnetism in Ho1-xDyxNi2B2C

The coexistence of the superconductivity and magnetism in the Ho1-xDyxNi2B2 C is studied by using Ginzburg-Laudau theory. This alloy shows the coexiste nce and complex interplay of superconducting and magnetic order. We propose a phenomenological model which includes two magnetic and two superconducti ng order parameters accounting for the multiband structure of this material . We describe phenomenologically the magnetic fluctuations and order and de monstrate that they lead to anomalous behavior of the upper critical field. The doping dependence of T-c in Ho1-xDyxNi2B2C showing a reentrance behavi or is analyzed yielding very good agreement with experimental data.