Structural and magnetic properties of polycrystalline La0.77Sr0.23Mn1-xCuxO3 (0 ≤ x ≤ 0.5) manganites

The effect or the substitution, for Mn With Cu in the polycrystalline La0.77Sr0.23Mn1-xCu3O3 (0 <= x <= 0.5) manganites upon the structural and magnetic properties has,, been investigated by means of X-ray diffraction (XRD)and magnetization measurements. The results indicate that replacing Mn by Cu in La0.77Sr0.23Mn1-xCu3O3 system led to a change in crystal structure at room tempetarure from rhombohedral phase ( R-3c space group 1) to orthorhombic phase (Pmna space group) at x >= 0.3. Paramagnetic to ferromagnetic phase transition at Curie temperature, T-c, is observed. It was round that substitution of Cu on the Mn site causes a reduction in T-c. The analysis of the crystallographic data suggested a strong correlation between structural and magnetism, for instance a relationship between a distortion of the MnO6 octahedron and file reduction in the Curic temperature. At x >= 0.3 the spin glass-like behaviour is evidence by a cup in the temperature-dependent magnetization, M(T), curves due to the appearance of antiferromagentic (AFM) superexchange interaction imposed with ferromagnetic (FM) double exchange (DE) interaction. The variation or the effective magnetic moment, mu(eff), upon Cu-doping level at B-site is analyzed in terms of structure phase transition. Magnetization at lower temperatures is less in the doped samples and decreases with increasing the Cu contents. A reduction in the saturated magnetic moments with increasing of the Cu substitution is observed in the concentration range x=0-0.2. (c) 2008 Elsevier B.V. All rights reserved.