A-site disorder induces magnetoresistance in Y and Sr co-doped La2/3-xYxCa1/3-ySryMnO3

ations of Y and Sr co-substituting for La and Ca at A site in La2/3Ca1/3MnO3 compound, La2/3-x.YxCa1/3-ySryMnO3, were synthesized successfully by solid-state reaction. X-ray diffraction shows there is only one phase with the dopants of Y and Sr within x <= 0.20 or y <= 0. 19. The lattice parameters along a-, b-, and c-direction remain almost unchanged with x <= 0.20. The bond angle of Mn-O-Mn increases from 151.9 degrees for x = 0 to 172.7 degrees for x = 0.20 monotonically, which indicates that the Jahn-Teller effect in MnO6 octahedron decreases with increasing x. The temperature dependence of resistance with/without magnetic applied were measured and fitted theoretically. The metal-to-insulator transition temperature, T-MI, decreases with increasing the Y content with x <= 0. 10 while T-MI, increases slightly with further increasing x. The Y-content dependence of magnetoresistance shows a parabolic behavior. The maximum MR value corresponds to x = 0.08-0. 10. We attributed these variations in the structure and transportation to the cation disorder due to the cation doping. (c) 2005 Elsevier B.V. All rights reserved.