Specific heat measurements of (Gd_1-xY_x)₃T compounds (T= Co and Ni) revealed a strong concentration dependence of the coefficient \gamma of the T-linear specific heat. In particular, the electronic specific heat coefficient \gamma of Y₃Co was found to be significantly lower (15 mJ/molK²) than that of isostructural Gd₃Co (110 mJ/molK²) and (Gd_0.2Y_0.8)₃Co (380 mJ/molK²). Such a behaviour can be attributed to the presence of a huge contribution of spin fluctuations in the d-electron subsystem induced by the f-d exchange interaction.

PACS numbers: 75.30.Mb, 74.25.Bt