Large Magnetic Entropy in Giant Magnetoresistive Amorphous Gadolinium Silicon

We report results of specific heat measurements from 5 to 70 K on thin films of the giant negative magnetoresistive spin glass $a$- ${\mathrm{Gd}}_x{\mathrm{Si}}_{1-x}$ and its nonmagnetic analog $a$- ${\mathrm{Y}}_x{\mathrm{Si}}_{1-x}$. The specific heat of $a$- ${\mathrm{Gd}}_x{\mathrm{Si}}_{1-x}$ samples is significantly greater than that of $a$- ${\mathrm{Y}}_x{\mathrm{Si}}_{1-x}$ samples below 50 K. The resulting magnetic entropy of $a$- ${\mathrm{Gd}}_x{\mathrm{Si}}_{1-x}$ exceeds the total calculated entropy available from Gd moments alone. We suggest that the additional entropy is provided by the interaction of barely localized electron spins with the Gd moments.