Effects of monovalent cation doping on the structure, microstructure, lattice distortion and magnetic behavior of single crystalline NdMnO3 compounds

Abstract

Pure and 15 mol% Na, K-doped NdMnO₃ compounds with perovskite structures are prepared by sol–gel method. Tiny single crystals are formed after sintering the compounds at 1000 °C. The effect of Na and K doping as well as the effect of sintering temperature on the formation and microstructure of NdMnO₃ are studied in detail by the Rietveld refinement technique using X-ray powder diffraction data. Single phase formation and single crystalline growth are also confirmed by high resolution transmission electron microscopy (HRTEM). Bond angles and bond lengths are calculated and shown by 3D diagrams. Monovalent doping induces noticeable changes in the microstructure and yields better structural stability in these compounds. Doping results in the change of Mn–O, Nd–O and Mn–O–Mn bond lengths which in turn reduces the lattice and octahedral distortion in the system along with an increase in the tolerance factor. The magnetic properties of these compounds are also modified as a result of doping. The temperature dependent magnetization results show that the Neel temperature of antiferromagnetic NdMnO₃ compound is 67.2 K and the Curie temperatures of ferromagnetic Nd_0.85Na_0.15MnO₃ and Nd_0.85K_0.15MnO₃ compounds are 99.1 K and 98.6 K respectively. Both 15% Na and K doping results in a similar T_C in doped NdMnO₃ compounds.