Doping effects on the structural, magnetic, and hyperfine properties of Gd-doped SnO2 nanoparticles

In this work we present the study of the structural, magnetic, and hyperfine properties of Gd-doped SnO2 nanoparticles synthesized by a polymer precursor method. The X-ray diffraction data analysis shows the formation of the rutile-type structure in all samples with Gd content from 1.0 to 10.0 mol%. The mean crystallite size is similar to 11 nm for the 1.0 mol% Gd-doped samples and it shows a decreasing tendency as the Gd content is increased. The analysis of magnetic measurements indicates the coexistence of ferromagnetic and paramagnetic phases for the 1.0 mol% Gd-doped sample; however, above that content, only a paramagnetic phase is observed. The ferromagnetic phase observed in the 1.0 mol% Gd-doped sample has been assigned to the presence of bound magnetic polarons which overlap to create a spin-split impurity band. Room-temperature 119 Sn Mossbauer measurements reveal the occurrence of strong electric quadrupole interactions. It has been determined that the absence of magnetic interactions even for 1.0 mol% Gd-doped sample has been related to the weak magnetic field associated to the exchange interaction between magnetic ions and the donor impurity band. The broad distribution of electric quadrupole interactions are attributed to the several non-equivalent surroundings of Sn4+ ions provoked by the entrance of Gd3+ ions and to the likely presence of Sn2+ ions. The isomer shift seems to be nearly independent of the Gd content for samples with Gd content below 7.5 mol%.