  We investigated experimentally and computationally the concentration
dependence of electronic specific heat coefficient $\gamma$ in
Y(Fe$_{1-x}$Co$_x$)$_2$ pseudobinary Laves phase system. The experimentally
observed maximum in $\gamma$($x$) around the magnetic phase transition was
interpreted within the local density approximation (LDA) combined with the
virtual crystal approximation (VCA). To explain the formation of the observed
maximum, we analyzed theoretically the dependence of the magnetic energy,
magnetic moments, densities of states, and Fermi surfaces on the Co
concentration. Furthermore, we carried out the calculations of density of
states at the Fermi level as a function of fixed spin moment. The calculated Co
concentration at which $\gamma$ takes the maximum value
($x_{\mathrm{max-LDA-VCA}}=0.91$) stays in good agreement with the measured
value ($x_{\mathrm{max-expt}} = 0.925$). We conclude that the observed maximum
in $\gamma(x)$ results from the presence of the sharp DOS peak in the vicinity
of the Fermi level.
