The effect of manganese doping on the superconducting transition temperature and the upper critical field of tin-molybdenum-sulfide

We have measured the superconducting transition temperature, Tc' and the upper critical field, Hc2 (T), of manganese-doped SnMo6S8 (MnxSn1_xMo6S8)' These samples had reproducible superconducting properties. They were characterized by x-ray powder diffractometry, optical microscopy. electron microscopy, and electron microprobe work. The transition temperature decreased slow1~ with increasing manganese content until x=O.06. It then increased until x=O.10. after which it fell slow1~ again. Manganese would norma11y have strong pair-breaking effects on the quasipartic1es, but our results provide an exception. X-ray Absorbtion Near-Edge Structure (XANES) measurements showed that the manganese exists as Mn+6 in our compound. Six of its seven valence electrons are transfered to the MoS 68 clusters of the compound. As Mn+6 has on1~ one valence electron in the 3-d orbital we expect it to be on1y slight1y magnetic. This helps to explain the low rate of T c depression. T for these compounds is dependent on the number c of electrons available to the mo1ibdenum atoms, and it peaks when this number is optimized. The peak in the T curve is c explained b~ considering the extra electrons transfered to the mo1ibdenum as the manganese doping is increased. H(T) curves upward from 0 to 15 kOe and is linear from c2 15 to 30 kOe. The curvature of the low-field section increases as the manganese doping is raised from x=O.O to x=0.06. Above x=0.06 the curvature does not change. The slope of the linear section does not vary with manganese content.U of I OnlyThesi