Theoretical Study of Phase Diagrams for Reentrant Superconducting Er$\text{}_{1-x}$Ho$\text{}_{x}$X, Er$\text{}_{1-x}$Gd$\text{}_{x}$X, Er$\text{}_{1-x}$Tm$\text{}_{x}$X, Ho$\text{}_{x}$Lu$\text{}_{1-x}$X, and Sm$\text{}_{1-x}$Er$\text{}_{x}$X (X = Rh$\text{}_{4}$B$\text{}_{4}$) Alloys

We consider a simplified version of the s-f model, supplemented by the intersite Cooper pairs interaction between conduction electrons with opposite spins to investigate ferromagnetic and superconducting properties of an alloy Re$\text{}_{1-x}^{(1)}$Re$\text{}_{x}^{(2)}$X (Re$\text{}^{(1),(2)}$ - rare earth elements, X = Rh$\text{}_{4}$B$\text{}_{4}$) using the virtual crystal approximation. For a suitable choice of the model parameters we can reproduce the phase boundaries of the experimentally measured phase diagrams for Er$\text{}_{1-x}$Ho$\text{}_{x}$X, Er$\text{}_{1-x}$Gd$\text{}_{x}$ X, Er$\text{}_{1-x}$Tm$\text{}_{x}$X, Ho$\text{}_{x}$Lu$\text{}_{1-x}$X, and Sm$\text{}_{1-x}$Er$\text{}_{x}$X alloys.