  With the aim of probing the effect of magnetic disorder in the
low-temperature excitations of manganites, specific-heat measurements were
performed in zero field, and in magnetic fields up to 9 T in polycrystalline
samples of La_{0.7-x}Y_{x}Ca_{0.3}MnO_{3}, with Y concentrations x=0, 0.10, and
0.15. Yttrium doping yielded the appearance of a cluster-glass state, giving
rise to unusual low-temperature behavior of the specific-heat. The main feature
observed in the results is a strong enhancement of the specific-heat linear
term, which is interpreted as a direct consequence of magnetic disorder. The
analysis was further corroborated by resistivity measurements in the same
compounds.
