Effective mass enhancement and spin-glass behaviour in CeCu4MnyAl1−y compounds

Abstract

We report on the magnetic ac/dc susceptibility and specific heat measurements for the CeCu4MnyAl1−y series of compounds with 0 ≤ y ≤ 1. All compounds investigated crystallize in the hexagonal CaCu5-type structure with the space group P6/mmm. The results reveal that the frustration of the interactions dominates and leads to a spin-glass (SG) behaviour with a linear change of the freezing temperature Tf as a function of y. The SG state has been confirmed by the frequency dependence of the ac magnetic susceptibility, the relaxation of the remanent magnetization and the split of the field-cooled–zero-field-cooled dc magnetic susceptibility. The electronic specific heat coefficient γ is enhanced for all y and increases with the Al content. Below a threshold at y ≈ 0.3, γ is large even if determined for temperatures above Tf; moreover the paramagnetic Curie–Weiss temperature θp changes sign to negative. These observations indicate the possible presence of the heavy fermion (HF) state, at least below y ≈ 0.3, and the possible coexistence of the SG and HF states down to y = 0, i.e. for the CeCu4Al compound. A tentative magnetic phase diagram for CeCu4MnyAl1−y has been constructed.