Structural, magnetic and magnetocaloric properties of nanostructured Pr0.5Sr0.5MnO3 manganite synthesized by mechanical alloying

Nanostructure ProzSr(0.5)MnO(3) compounds were elaborated by mechanical milling in a planetary high energy ball mill at various milling times followed by high temperature sintering under air at 1400 degrees C for 20 h. The phase structure, the morphology, the magnetic and magnetocaloric properties of the powders were characterized by X-ray diffractometry, scanning electron microscopy and a vibrating sample magnetometer. Rietveld refinement of the X-ray diffraction patterns shows that all specimens crystallize in the tetragonal system with I4/mcm space group. Increasing the milling time up to 16 h, the average crystallites size decreases to the nanoscale (similar to 36 nm). During the intermediate stage of milling, significant changes occur in the morphology of the powder particles, due to the severe plastic deformation. Significant refinement in particle size was found evident at the final stage of milling (similar to 2 mu m). From magnetic measurements, it was found that all samples present two magnetic transitions as a function of temperature. The Curie temperature Tc decreases with increasing milling time. Moreover, it was revealed that the antiferromagnetic domains fractions highly dependent on crystallites sizes. A large magnetocaloric effect and an important value of the relative cooling power around Neel temperature was observed in all samples. These characteristics may be related to the first ordered nature of this transition. Moreover, the magnetic entropy change and the relative cooling power were increased with decreasing crystallites sizes.