Abstract
Recent data suggest that the high- compound presents considerable difficulties for conventional theories of magnetic pair breaking. We report results of x-ray diffraction, superconducting-quantum-interference-device magnetization, and resistivity measurements for single-phased polycrystalline specimens of (M=Ce, Y, La, and Sr) for various x and y. In each case, the magnetic ions are diluted by a nonmagnetic species: isovalent and , or nonisovalent and . Rare-earth magnetic order occurs below 6 K in ; isovalent dilution with M=Y results in a depression of the Néel temperature at an initial rate (1/)(/dx)=-0.0110/at. %, a result that can be well described by a simple theory of magnetic dilution. Isovalent dilution with M=La reveals a small steric effect. Nonisovalent dilutions are interpreted in terms of concentration-dependent exchange interactions; electron and hole dopings result in depression and enhancement of the rare-earth exchange coupling, respectively. Our results (scrj≲6 meV) indicate that the coupling between rare-earth ions and superconducting electrons is probably much smaller than previously suggested, and that conventional magnetic pair-breaking theory adequately describes these materials. Some magnetic features suggestive of a subtle transition in the range x=0.10–0.15 in the insulating M=Ce series are also observed.
- Received 1 August 1991
DOI:https://doi.org/10.1103/PhysRevB.45.2311
©1992 American Physical Society