Fluctuant Magnetism in Metal Oxide Nanocrystals Capped with Surfactants

We demonstrate experimentally that magnetism in ZnO, TiO2, CeO2, and SnO2 nanocrystals (NCs) has a fluctuant nature that varying with capping surfactant type and concentration. By developing a forced hydrolysis approach with additional post-processing for the synthesis and surfactant capping of these NCs, we effectively avoid the influence of size, shape, and magnetic impurities on the magnetic behavior of NCs, thus revealing the systematic influence of the capping surfactants on the NC magnetism. The x-ray photoelectron spectroscopy results and theoretical calculations clearly show that the magnetism fluctuation with surfactant concentration can be attributed to the periodic variation of spins, which arises from the concentration dependent electron transfer from surfactants to NCs. Our results not only explain the previously reported seemingly irregular magnetism induced by capping surfactants, but also provide an effective approach to tune or optimize the NC magnetism. This is an author-produced, peer-reviewed version of this article. The final, definitive version of this document can be found online at Physical Review B: Condensed Matter and Materials Physics, published by American Physical Society. Copyright restrictions may apply. DOI: 10.1103/PhysRevB.88.085437.