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Abstract:
Dilute (La1−x Nd x )Sn3 alloys with 0.01<x<0.15 are characterized by determination of the superconducting transition temperatureT c as well as low temperature measurements of the specific heat and inelastic neutron scattering. As an important result of these experiments we found that the Nd impurities in LaSn3 exist as stable trivalent ions, in contrast to all other light rare earths. In addition, specific heat and neutron scattering results revealed the scheme of crystal field (CF) levels of Nd3+.
Using this level scheme, the concentration dependence of the superconducting transition temperature,T c (x), could be quantitatively fitted up tox≃9 at % by the theory of Keller and Fulde [J. Low. Temp. Phys.4, 289 (1971)]. From the relatively high initial slope ofT c (x) we inferred that — besides isotropic spin exchange — other pair-breaking processes are important.
In contrast toT c (x), the reduced specific heat jumpsΔC/ΔC 0 as a function ofT c /T c0 (whereT c0 andΔC 0 refer to LaSn3) were found to lie considerably below the theoretical curve for isolated Nd3+ ions. This is explained by Nd—Nd interactions resulting in a mean Zeeman splitting (<k B T c ) of the CF ground state, which could be directly observed in the form of broadened Schottky humps in the normal state specific heats.
