Low temperature properties of (La,Nd)Sn3 alloys

Dilute (La_1–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 tox9 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 jumpsC/C ₀ as a function ofT _c /T _c0 (whereT _c0 andC 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.