Role of A site doped rare earth (Gd3+ and Ho3+) ions in the lattice structure and magnetic properties of biphasic La2−xRExNiMnO6 (RE = Gd, Ho, x = 0.1) double perovskites

Abstract

The doping effects of a small amount of RE (Gd and Ho) atoms at A (La) sites of La2NiMnO6 double perovskite have been studied by preparing the materials using mechanical alloying of oxide powders and thermal treatment (800–1200 °C), and a direct sintering of the oxide powders at 1300 °C. The synchrotron x-ray diffraction patterns have been used to confirm the formation of single (monoclinic) phase or bi-phased lattice structure depending on thermal treatment temperature. The bi-phased samples are consisting of primary monoclinic phase (P 21/n space group) and secondary orthorhombic phase (Pnma space group). The x-ray photoelectron spectroscopy has confirmed the presence of trivalent La, RE ions, and mixed-valence state of Ni and Mn ions in the samples. The existence of bi-phasic lattice structure and mixed-valence state of Ni and Mn ions have determined magnetic properties. The monoclinic phase has shown ferromagnetic Curie point around 280 K, which has been reduced to low temperature by Gd and Ho doping. The orthorhombic phase has shown weak ferro/ antiferromagnetic spin ordering temperature around 150 K. The experimental results in RE doped La2NiMnO6 double perovskite support a strong correlation between lattice structure and magnetic properties, which depend on doping of RE ions at A sites, electronic charge state of Ni and Mn ions, structural phase components and anti-site disorder of Mn/Ni ions at octahedral sites.