Abstract
Bulk nanocrystalline samples of La(0.65)Ce(0.05)Sr(0.3)Mn(1-x) Cu (x) O(3) (0 ≤ x ≤ 0.15) manganites are prepared by the sol-gel based Pechini method. The effect of the substitution for Mn with Cu upon the structural and magnetic properties has been investigated by means of X-ray diffraction (XRD), Raman spectroscopy and dc magnetization measurements. The structural parameters obtained using Rietveld refinement of XRD data showed perovskite structures with rhombohedral (R3̄c) symmetry without any detectable impurity phase. Raman spectra at room temperature reveal a gradual change in phonon modes with increasing copper concentration. The analysis of the crystallographic data suggested a strong correlation between structure and magnetism, for instance a relationship between a distortion of the MnO(6) octahedron and the reduction in the Curie temperature, T (c). A paramagnetic to ferromagnetic phase transition at T (C) is observed. The experimental results confirm that Mn-site substitution with Cu destroys the Mn(3+)-O(2-)-Mn(4+) bridges and weakens the double exchange (DE) interaction between Mn(3+) and Mn(4+) ions, which shows an obvious suppression of the FM interaction in the La(0.65)Ce(0.05)Sr(0.3)Mn(1-x) Cu (x) O(3) matrix. The maximum magnetic entropy change -ΔS (max) (M) is found to decrease with increasing Cu content from 4.43 J kg(-1) K(-1) for x = 0 to 3.03 J kg(-1) K(-1) for x = 0.15 upon a 5 T applied field change.