Effect of strontium deficiency on the structural, magnetic and magnetocaloric properties of La0.65Eu0.05Sr0.3−xMnO3 (0 ≤ x ≤ 0.15) perovskites

Abstract

We have investigated the effect of nominal strontium deficiency on the structure, magnetic and magnetocaloric properties of La_0.65Eu_0.05Sr_0.3−xMnO₃ (x = 0, 0.10 and 0.15) perovskites. The nanocrystalline samples were prepared by the 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 Rc, no. 167). Raman spectra at room temperature reveal a gradual change in phonon modes with increasing nominal strontium deficiency. All the 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 ΔS^max_M peaks led to enhanced relative cooling power (RCP) in the Sr-deficiency samples of up to 22% over that of La_0.65Eu_0.05Sr_0.3MnO₃. La_0.65Eu_0.05Sr_0.15MnO₃ 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_0.65Eu_0.05Sr_0.3−xMnO₃ materials are strongly suggested for use as active refrigerants for magnetic refrigeration technology near and above room temperature.