Lattice effect on the magnetic and magneto-transport properties of (La1/3Sm2/3)0.67Ba0.33-xSrxMnO3 (x=0.0, 0.1, 0.2 and 0.33) compounds

The effect of substituting Sr for Ba on the magneto-transport and magnetic properties of (La1/3Sm2/3)(0.67)Ba0.33MnO3 system, has been investigated. The samples, (La1/3Sm2/3)(0.67)Ba0.33-xSrMnO3 (x=0,0, 0.1, 0.2 and 0.33), synthesized by citrate gel route, crystallize in an orthorhombic structure (space group Pnma, no. 62). The unit cell volume decreases while the metal-insulator transition temperature (T-MI) increases with increasing Sr content. The localization of charge carriers occurs at low temperatures and becomes more pronounced with decreasing Sr content which leads to an enhancement of resistivity. This could be understood by the variation of Mn-O-Mn bond-distance and angle. Reappearance of semiconducting behavior (d rho/dT< 0) is observed only in samples with x = 0 and x = 0.1 below certain temperature (T< T-MI). These samples exhibit thermal irreversibility behavior for a field-cooled (FC) and zero-field-cooled (ZFC) magnetization data in a magnetic field of 100 Oe. This is ascribed to the competition between the superexchange and double exchange interactions. The change in physical properties has been correlated to chemical parameters such as ionic radii, tolerance factor, electronegativity and variation in Mn-O-Mn angle. (c) 2006 Elsevier B.V. All rights reserved.