Sol–gel synthesis and structural-magnetic properties of Ba2-xAxFeMoO6 (A = Ag, Sm): effects of partial A-site substitution

Double perovskite oxides are promising candidates for spintronic and magnetic applications because their magnetic properties can be effectively tailored through ionic substitution. In this work, the effects of non-magnetic Ag + and magnetic rare-earth Sm 3+ substitution at the Ba site of Ba 2 FeMoO 6 were systematically compared for the first time at the same doping level (x = 0.05). Ba 2−x A x FeMoO 6 (A = Ag, Sm; x = 0.0 and 0.05) compounds were synthesized using the sol–gel method to investigate the influence of these dopants on the structural and magnetic properties of Ba 2 FeMoO 6 . The crystal structure, morphology, chemical states, and magnetic properties were characterized using X-ray diffraction with Rietveld refinement, FE-SEM, FTIR spectroscopy, XPS, and magnetic measurements. Structural analysis confirmed that all samples crystallized in a single-phase cubic structure with the Fm-3m space group. Although Ag + and Sm 3+ substitution did not change the crystal symmetry, slight modifications in the lattice parameters, unit-cell volume, and bond lengths were observed. FE-SEM images revealed an increase in porosity after doping, while FTIR spectra indicated changes in the vibrational modes associated with the MoO 6 octahedra. XPS analysis confirmed the coexistence of Fe 2+ /Fe 3+ and Mo 5+ /Mo 6+ mixed valence states, which are essential for the double-exchange interaction. Magnetic measurements showed that both doped samples exhibited lower magnetization than the undoped compound. In contrast, Ag + substitution reduced the magnetic transition temperature, whereas Sm 3+ substitution increased it. These variations are attributed to dopant-induced structural distortions and changes in bond lengths, which modify the magnetic exchange interactions. The results provide new insights into the distinct roles of non-magnetic and magnetic dopants in tuning the structural and magnetic behavior of Ba 2 FeMoO 6 double perovskites.