Fluctuations and the ferromagnetic instability in YFe₂Al₁₀: The role of Fe stoichiometry

YFe₂Al₁₀ forms in a well-ordered crystal structure, with a unique site for the magnetic atom Fe. At elevated temperatures YFe₂Al₁₀ behaves electronically as a good metal. At low temperatures on the other hand, signatures of correlated behavior develop and eventually non-Fermi-liquid scaling dominates all of the physical properties: the electrical resistivity develops a negative temperature coefficient below 20K, and the specific heat C_p(T)/T and χ(T) both assume a power-law increase upon lowering the temperature below ≃3K. Lowest temperature studies have failed to find magnetic ordering in YFe₂Al₁₀ in spite of compelling evidence that there is impending order in this compound and that it is indeed of ferromagnetic character. Here we report on measurements of thermal and electronic transport as well as heat capacity studies on the series of compounds YFe_2+δAl₁₀ with δ≤|0.1|, with the purpose of testing the stability of the low-temperature divergences in physical properties against off-stoichiometric Fe.