INFLUENCE OF PHASE-COMPOSITION ON THE REENTRANT SUPERCONDUCTING PROPERTIES OF TM2FE3SI5

The compound Tm2Fe3Si5 is the only known reentrant superconductor in w hich superconductivity is destroyed at the antiferromagnetic transitio n. Widely differing behavior has been reported in the literature regar ding the occurrence of superconductivity ranging from transition tempe ratures around 1.7 K at atmospheric pressure to no superconductivity e xcept under applied hydrostatic pressure. In order to clarify this sit uation, we carried out ac-susceptibility measurements under applied pr essure and magnetization measurements as a function of phase compositi on within the homogeneity range of the compound and on multiphase samp les. For single-phase samples, T-c decreases strongly in the whole pre ssure range with growing stoichiometric ratio Fe/Si. For multiphase sa mples, a shift of the T-c vs pressure curves to lower pressure values was observed. The high-temperature part of the susceptibility follows a Curie-Weiss law independent of phase composition which amounts to an effective magnetic moment per Tm atom of 7.0 mu(B). With our results we are able to explain all the observed sample dependence of T-c with a combination of substitution effects in the homogeneity range of this compound and internal stress effects caused by impurity phases.