Breakdown of deGennes scaling in (R(1-x)R'(x))Ni2B2C compounds

The superconducting transition temperatures (T-c) and Neel temperatures (T-N) have been determined for thirty (R(1-x)R(x)')Ni2B2C Single crystals. For T-c > T-N, deviations from de Gennes scaling occur that are probably due to crystalline electric field effects. For T-c < T-N there is a complete breakdown of de Gennes scaling. In (D(1-x)R(x)')Ni2B2C, R' = Lu suppresses T-c an order of magnitude more rapidly than R' = Ho. This breakdown is inferred to arise from pair breaking by collective magnetic excitations.