Specific heat and magnetic properties of Nd0.5Sr0.5MnO3 and R0.5Ca0.5MnO3 (R=Nd, Sm, Dy, and Ho)

Magnetization and specific heat measurements of Nd0.5Sr0.5MnO3, Nd0.5Ca0.5MnO3, Sm0.5Ca0.5MnO3, Dy0.5Ca0.5MnO3, and Ho0.5Ca0.5MnO3 samples were performed. Near the charge ordering (CO) and ferromagnetic transition temperatures, the specific heat curves showed peaks superimposed to the characteristic response of the lattice oscillations. These peaks allowed us to estimate the entropy variation for each phase transition. The entropy variation corresponding to the CO transition was higher than the one corresponding to the ferromagnetic transition. Furthermore, specific heat measurements in presence of a 9 T magnetic field showed that this field was not strong enough to affect the specific heat in the CO phase transition region. Our results suggest that the CO phase is very stable and almost independent of magnetic fields. (C) 2003 American Institute of Physics.