Depression of Tc by nonmagnetic impurities in antiferromagnetic superconductor with Tc< TN

Abstract

Theoretical considerations show that nonmagnetic impurities (which in conventional superconductors are not expected to have much influence on T c) should depress T c in antiferromagnetic superconductors with T c< T N. DyNi 2B 2C ( T c=6.5 K, T N=11 K) and ErNi 2B 2C ( T c =10.5 K, T N =6.5 K ) form an ideal pair of antiferromagnetic superconductors, with T c< T N and T c> T N, respectively, to investigate this effect experimentally which is the aim of the present work. Our most important finding is that in Y 1− x Dy x Ni 2B 2C, dilute substitution of Y results in a decrease of T c (Δ T c∼−2.5 K for x=0.9) in direct contrast to Y 1− x Er x Ni 2B 2C, where substitution of Y results in an increase of T c (Δ T c∼+0.3 K for x=0.9). Although depression of T c in DyNi 2B 2C by nonmagnetic Lu ions has been reported, that report did not consider the above-mentioned theoretical consideration. Our work points out the importance of nonmagnetic impurities in magnetic superconductors.