Synthesis, structure and magnetic properties of Ti doped La2MnNiO6 double perovskite

Abstract

We report sol-gel synthesis, structural characterization and magnetic properties of La2Mn1–xTixNiO6 (0 ≤ x ≤ 1.0). Ti doping removed the biphasic structure of La2MnNiO6 by suppression of rhombohedral structure and all the Ti containing samples crystallized in monoclinic P21 / n symmetry. La2MnNiO6 exhibits multiple magnetic transitions. The high temperature ferromagnetic transition of La2MnNiO6 gradually shifted to lower temperatures with increase in Ti doping. La2TiNiO6 (x = 1.0) does not show any long-range magnetic ordering. The suppression of magnetic transition by Ti doping is ascribed to the destruction of Mn4+ – O – Ni2+ superexchange interaction. However, the signature of ferromagnetic phase persists up to 70 % Ti doping, indicating the robustness of magnetic ordering in La2MnNiO6. These results suggest that the addition of Ti4+ truncates the ferromagnetic Mn4+ – O – Ni2+ superexchange path and it likely promotes ferromagnetic cluster formation. The robustness of ferromagnetic state towards Ti substitution compared to the simple perovskite or spinel structure can be attributed to cationic ordering in double perovskite structure. Both the pure and Ti-doped samples exhibit magnetic frustration at lower temperatures due to partial cationic disordering. The absence of long-range ordering in La2TiNiO6, unlike La2TiCoO6 or Pr2TiCoO6, could be related to cationic disordering.