Anomalous low-temperature specific heat of charge-ordered La0.5Ca0.5MnO3

We report a study of the specific heat, resistivity, and magnetization of La1-xCaxMnOx for x = 0.47, 0.5, 0.53 with and without an applied magnetic field. In zero (earth) field we find that the charge-ordered materials (x = 0.5,0.53) have extra entropy of nonmagnetic origin at low temperature when compared to metallic and ferromagnetic compositions (x = 0.47,0.2). For the x = 0.5 compound the specific heat does not change in a 8.5 T field even though the resistivity decreases ten orders of magnitude.