Synchrotron-based XAS on structure investigation of La0.99-xSrx(Na, K, Ba)0.01MnO3 nanoparticles: Evidence of magnetic properties

This work presents the structural study of La_0.99-xSr_x(Na, K, Ba)_0.01MnO₃ or LSAM nanoparticles synthesized using thermal-hydro decomposition method where A denotes Na, K, Sr and Ba, respectively. The effect of ionic radii size of A dopants or r_A from the substitution of A for La and Sr on the MnO₆ octrahedral structure, where the average size of the cations occupying in A-site or <r_A> is fixed at ∼ 1.24 Å, is focused. The LSAM nanoparticles are carefully studied using X-ray diffraction (XRD) including Rietveld refinement and X-ray Absorption Spectroscopy (XAS) including X-ray Absorption Near edge Structure (XANES) and X-ray Absorption Fine Structure (EXAFS). The Rietveld refinement shows all nano-powder samples have rhombohedral structure. By XANES technique we found that the effect of A substitutions at A-site causes a slight change of mean oxidation state of Mn between 3.54 and 3.60. Furthermore, the structural distortion of MnO₆ octrahedral in samples is analysed and obtained from EXAFS. The observed trend of ferromagnetism for all LSAM samples can be clearly explained by evidences of A-site doping, structural distortion around Mn atoms and mixing Mn³⁺/Mn⁴⁺ valence states.