Effect of hydrostatic and chemical pressure on the exchange interaction inmagnetic borocarbide superconductors

The investigation of pair-breaking effects in magnetic rare-earth nickel bo rocarbide superconductors reveals a considerable increase of the magnetic e xchange integral J(sf) by hydrostatic as well as chemical pressure. In both , J(sf) is governed by the R-C distance (or lattice constant a) and is desc ribed quantitatively by a simple phenomenological model. Thereby, just two parameters J(sf0) = 31 meV and Delta J(sf)/Delta a = 165 meV/Angstrom expla in well the influence of chemical pressure upon the initial depression rate s of T-c in solid solutions R1-x'R2Ni2B2C with R = Gd, Tb, Dy, Ho and R' = Y and Lu.