Long-range ferromagnetic order induced by a donor impurity band exchange in SnO2:Er3+ nanoparticles

In this work, the structural and magnetic properties of Er-doped SnO2 (SnO2:Er) nanoparticles are reported. The SnO2:Er nanoparticles have been synthesized by a polymer precursor method with Er content from 1.0% to 10.0%. X-ray diffraction results indicate the formation of only the rutile-type structure in all samples. The estimated mean crystallite size shows a decrease from similar to 10 to similar to 4 nm when the Er content is increased from 1.0% to 10.0%. The particle size values have been corroborated by transmission electron microscopy technique. The thermal dependence of the magnetization is consistent with the 3+ oxidation state of erbium ions for all samples. A strong paramagnetic-like behavior coexisting with a ferromagnetic phase has been determined for samples with Er content below 5.0%. Above this concentration, only a paramagnetic behavior has been determined. Isothermal magnetization curves are consistent with the occurrence of long-range ferromagnetic order mediated by donor electrons forming bound magnetic polarons which overlap to produce a spin-split impurity band. (C) 2013 AIP Publishing LLC.