Penetration Depths of Antiferromagnetic Superconductors SmRh sub 4 B sub 4 and NdRh sub 4 B sub 4

We have investigated the surface impedance penetration depth , lambda, both experimentally and theoretically of two antiferromagnetic superconductors, SmRh sub 4 B sub 4 and NdRh sub4 B sub 4 which exihit quite different temperature dependencies of the upper critical field arising from two different mechanisms of the modification of the superconductivity by the presence of the antiferromagnetism: the antiferromagnetic molecular field effect and the spin-fluctuation effect. It has been shown the importance of the fluctuation effect for SmRh sub 4 B sub 4 (lambda sup -1 increases more rapidly below T sub N) in contrast to NdRh sub 4 B sub 4 where the molecular field effect is more significant ( lambda decreases below T sub N).