Abstract
Magnetic ions (Mn) were substituted in single crystals resulting in a strong pair-breaking effect. The superconducting transition temperature, , in has been found to be rapidly suppressed at an initial rate of , leading to a complete suppression of superconductivity at about 2% Mn substitution. This reflects the strong coupling between the conduction electrons and the local moments, predominantly of magnetic character, since the nonmagnetic ion substitutions, e.g., with Al or C, suppress much less effectively (e.g., ). The magnitude of the magnetic moment ( per Mn), derived from normal state susceptibility measurements, uniquely identifies the Mn ions to be divalent, and to be in the low-spin state . This has been found also in x-ray absorption spectroscopy measurements. Isovalent substitution for mainly affects superconductivity through spin-flip scattering reducing rapidly and lowering the upper critical field anisotropy at from 6 to 3.3 ( Mn), while leaving the initial slope near unchanged for both field orientations.
2 More- Received 24 October 2005
DOI:https://doi.org/10.1103/PhysRevB.73.174520
©2006 American Physical Society