Interaction of a dilute 111In-111Cd probe in the samples of CeRu2 synthesized at high pressure; influence of admixtures at Ce and Ru sites

Full text: It has been established, that by the method of the perturbed angular γγ-correlations (PAC), that in the cubic (C15( Laves phase CeRu2 the 111In-111Cd nuclear probe at a pressure of 8 GPa, the PAC spectrum consisted of two nearly equally populated fractions with vQ=220 MHz and 150 MHz. Both fractions were characterized by very low asymmetry parameters and very narrow frequency distributions around the quoted values. The second component could not be assigned to Ce sites which have cubic symmetry where the electric field gradient should be zero. As long as no alien structures were revealed by the X-ray diffraction analysis of the samples, we had to describe this fraction to the same substitutional sites in the Ru sublattice. In attempts to understand the nature of the second fraction (150 MHz) we have performed the PAC studies of influence of different admixtures at Ce and Ru sites on QI of 111Cd. Here we summarize data on samples (Ce1-xLax)Ru2, (Ce1-xxCox)Ru2, Ce(Ru1-xCox)2, and Ce(Ru1-xInx)2. In particular, it was shown that small admixtures of Ca and Co did not influence the 220 MHz fraction, but heavily distorted QI of 111Cd in the second fraction inducing a broad distribution of quadrupole frequency around its mean value. On the other hand, a small, though macroscopic (0.3%), admixture of In completely eliminated the low frequency component in the PAC spectrum where the unique 220 MHz fraction was present. Evidently, the 111In-111Cd probe at extremely low concentrations (≅108) senses certain variation in the electron structure of CeRu2 brought about by the synthesis at high pressure, which manifests itself in changes of some macroscopic properties of this phase - decrease of the superconducting transition temperature Tc from 6.2 K to 5.0 K and increase of the Ru magnetic moment by about three orders of magnitude