The specific heat jump of superconducting La1-xTbxAl2 related to crystal electric field splitting of the Tb3+ levels

Measurements of the specific heat jump Δc(Tinc) were performed on superconducting La_1-xTb_xAl₂ compounds in order to investigate the pairbreaking effect of Tb³⁺ ions in the LaAl₂ host. The results deviate from the Abrikosov-Gorkov theory for superconductors with magnetic impurities. Taking into account the crystal field level structure of Tb³⁺ in LaAl₂ the results can be qualitatively understood within the model of Fulde, Keller and Peschel. According to calculations published by Müller-Hartmann and Zittartz an influence of the Kondo effect can be ruled out.