MAGNETIC PHASE TRANSITION AND MAGNETOCALORIC EFFECT OF RE0.7Sr0.3MnO3 POLYCRYSTALLINE MATERIALS

In this report, we present some results of the magnetic phase transition nature and magnetocaloric effect of four polycrystalline ceramics of RE0.7Sr0.3MnO3 with RE = La, Pr, Nd and Sm, which were prepared by solid phase reaction method. X-ray diffraction data shows that all samples are single phase of RE0.7Sr0.3MnO3. The sample with RE = La belongs to the rhombohedral structure (space group: R3-c), whereas the other remaining samples belong to the orthorhombic one (space group: Pbnm). We pointed out that the difference in ionic radius at the RE site plays an important role in modifying the nature and Curie temperature (TC) of the ferromagnetic-paramagnetic phase transition of RE0.7Sr0.3MnO3 compounds. Namely, the RE = Nd sample has the characteristics of the first-order magnetic phase transition with TC = 242 K. Meanwhile, for RE = La, Pr, and Sm, the materials exhibit the characteristics of the second-order magnetic phase transition with TC = 360, 262, and 98 K, respectively. Among these, the magnetic phase transitions of two compounds with RE = Pr and Nd occur near room temperature with very large magnetocaloric effects. The values of the maximum magnetic entropy changes are higher than 3 J/kgK under magnetic field change of 10 kOe, suggesting their potential application in the field of civil magnetic refrigeration. The nature of the magnetic phase transition and the characteristic quantities related to the magnetocaloric effects of the RE0.7Sr0.3MnO3 compounds were studied and discussed in detail through the temperature and magnetic field dependences of the magnetization data.