Specific Heat of Single Crystalline Nd$_{0.5}$Sr$_{0.5}$MnO$_{3}$

Substantial studies of magnetization and specific heat on Nd$_{0.5}$Sr$_{0.5}$MnO$_{3}$ have demonstrated the existence of a charge ordering (CO), ferromagnetic (FM), antiferromagnetic (AFM) transitions. In this work, the specific heat of two single crystalline Nd$_{0.5}$Sr$_{0.5}$MnO$_{3}$ samples, one containing $^{16}$O and the other highly concentrated $^{18}$O, was measured as a function of temperature, from 3K to 300K, at both zero and 50 kOe applied field. Measurements were done using a Quantum Design Physical Property Measurement System (PPMS) with Specific Heat option. The FM transition was found to depend on the isotope mass, which seems to agree with previous works. The CO transitions was observed as a sharp peak at the CO temperature (T$_{co}$), which seems to depend strongly on field, oxygen isotope mass, and thermal cycling history.