A-site disorder induces magnetoresistance in Y and Sr co-doped La2/3-xY xCa1/3-ySr yMnO3

Cations of Y and Sr co-substituting for La and Ca at A site in La2/3Ca1/3MnO3 compound, La2/3-xY xCa1/3-ySr yMnO3, 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 deg for x = 0 to 172.7 deg 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