Extra T-linear specific heat contribution induced by the f-d-exchange in Gd-Ni binary compounds

Specific heat measurements performed for Gd-Ni binary compounds with 1: 2, 1: 1 and 3: 1 stoichiometry have revealed an additional contribution to the coefficient gamma of the T-linear term of the low-temperature specific heat in comparison with that obtained for isostructural paramagnetic counterparts R-Ni (R = Y, Lu, La). This extra contribution Delta gamma is found to grow linearly with increasing Gd concentration from nearly zero for GdNi5 up to Delta gamma approximate to 21.5 mJ g-at.(-1) K-2 for Gd3Ni. To explain the appearance of Delta gamma and its dependence on the strength of the f-d exchange interaction in Gd-rich binary compounds with Ni a new mechanism enhancing the effective mass of conduction electrons is suggested. The increased gamma value in Gd-containing compounds is attributed to spin fluctuations induced by the f-d exchange interaction in the hybridized 3d-5d electron subsystem.