Abstract:
In this thesis, coexistence of superconductivity and ferromagnetism states in cuprate based
superconductor Y1−xPrxBa2Cu3O7−δ was investigated theoretically. A model Hamiltonian
which represents the competing energies in the system was developed. This model
Hamiltonian was solved employing the equation of motion approach of the retarded
Green’s function. From the Green’s functions of the Hamiltonian, we obtained the
mathematical expressions for superconducting transition temperature (Tc), magnetic order
transition temperature (Tm), superconducting order parameter (∆SC) and magnetic order
parameter η. The suppression of superconductivity by Praseodymium, including hole
filling by charge transfer from Pr to the CuO2 planes, hole localizations, magnetic pair
breaking. Using the experimental and theoretical values and by considering plausible
approximations of the parameters in the obtained expressions, the phase diagrams of
superconducting transition temperature versus Pr concentration and magnetic ordering
temperature versus magnetic ordering parameter are plotted. By merging the two graphs,
we have got a region in which both superconductivity and ferromagnetism coexist in
Y1−xPrxBa2Cu3O7−δ system. Superconductivity appears together with ferromagnetism
continue only until the ferromagnetic effect is not sufficiently large .
