We have investigated the effect of nominal strontium deficiency on the structure, magnetic and magnetocaloric properties of La 0.65 Eu 0.05 Sr 0.3-x MnO 3 (x=0, 0.10 and 0.15) perovskites.The nanocrystalline samples were prepared by sol-gel-based Pechini method. Rietveld refinement of the X-ray diffraction patterns, shows the formation of single-phase compositions with rhombohedral symmetry (space group R-3c, no. 167). Raman spectra at room temperature reveal gradual change in phonon modes with increasing nominal strontium deficiency. All samples undergo paramagnetic-ferromagnetic (PM-FM) transition. The Curie temperature decreases linearly with increasing x and changes from 355 K for x = 0 to 280 K for x = 0.15. Arrott plot analyses and a universal curve method were applied for studying the order of the magnetic transition in this system, found to be of second order. As strontium deficiency content increased further, peak entropy values were seen to decline. However, a simultaneous broadening of the max M S ∆ peaks led to enhanced relative cooling power (RCP) in the Sr-deficiency samples of up to 22% over that of La 0.65 Eu 0.05 Sr 0.3 MnO 3 . La 0.65 Eu 0.05 Sr 0.15 MnO 3 exhibits the largest RCP value of 283 J.kg -1 at 280 K among the compounds investigated up to 5 T applied field. Through these results, La 0.65 Eu 0.05 Sr 0.3-x MnO 3materials are strongly suggested for the use as active refrigerants for magnetic refrigeration technology near and above room temperature.

Bulk nanocrystalline samples of La0.65Ce0.05Sr0.3Mn1−xCuxO3 (0 ≤ x ≤ 0.15) manganites are prepared by the sol–gel based Pechini method.

International audiencePolycrystalline samples of (Nd1−xCex)0.7Sr0.3MnO3 (x=0, 0.10 and 0.20) were prepared by a high-temperature solid-state reaction technique. The X-ray diffraction study has shown that all the samples exhibit a single phase with orthorhombic structure (space group Pnma). From the resistivity data, it is found that all the samples show metal to semiconductor transition and the transition temperature decreases with the Ce doping. The complex impedance has been investigated in the temperature range 80–320 K and in the frequency range 40 Hz–1 MHz. AC conductance analyses indicate that the conduction mechanism is strongly dependent on temperature and frequency. The impedance plane plot shows semicircle arcs at different temperatures and an electrical equivalent circuit has been proposed to explain the impedance results. The activation energies obtained from the conductance is slightly higher than that from time relaxation analyse

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