Crystal Structure and Magnetic Properties of (Co-Ag) co-doped SnO2 Compounds

Pure SnO2, Sn0.94Co0.06O2, Sn0.91Co0.06Ag0.03O2, and Sn0.88Co0.06Ag0.06O2 compounds were synthesized by the solid-state reaction method. The structural characterization of these compounds by recording X-ray diffraction patterns (XRD) and analyzing them using Rietveld refinement analysis shows that these materials are in single-phase tetragonal rutile structure with typical lattice constant of a = b = 4.7385 Å and c = 3.1871 Å for SnO2 compound. SEM images show the formation of homogenous nanometer range spherical particles. Temperature variation of magnetization (M-T) measurements show a typical diamagnetic behavior in parent compound, while ferromagnetic (FM) to paramagnetic transition is observed in Sn0.94Co0.06O2 compound with a Curie temperature of 232.5 K. The (Co-Ag) co-doped SnO2 compounds undergo double ferromagnetic transitions. These compounds exhibit first FM transition below 620 K and another FM transition at 1108 K and 1052 K, respectively for Sn0.91Co0.06Ag0.03O2 and Sn0.88Co0.06Ag0.06O2 compounds. The measurement of magnetic hysteresis (M-H) curves at room temperature indicates the increase in coercivity and saturation magnetization values with the increase of (Co-Ag) co-doping concentration. The observed ferromagnetism was discussed based on the exchange interaction between Co2+ and Co3+ ions via oxygen vacancies.