Magnetic heat capacity in lanthanum manganite single crystals

The heat capacity of single crystal La0.7D0.3MnO3, where D=Ca, Sr, has been measured through the Curie point in fields up to 70 kOe. The magnetic cont ribution of the Ca sample exhibits a sharp heat capacity peak at T(C)simila r or equal to 218 K in zero field. The peak broadens and decreases in heigh t with increasing field but, unlike an ordinary ferromagnet, the peak shift s substantially in temperature. As a consequence, the heat capacity data ca nnot be collapsed into a single scaling function. These features indicate t hat the transition is not an ordinary second-order ferromagnetic transition . Preliminary heat capacity data from the Sr-doped single crystal, with T(C )similar or equal to 360 K, do not exhibit the same shift in peak position with applied field. We attribute the difference in behavior between Ca- and Sr-doped samples to a change in the nature of the phase transition as T-C lowers. (C) 2000 American Institute of Physics. [S0021-8979(00)42608-3].