Oxygen diffusion and vacancy migration thermally-activated govern high-temperature magnetism in ceria.

Several experimental works currently demonstrate that metallic nano-oxides and carbon nanomaterials expected to be diamagnets, in fact, behave as ferromagnets at room temperature. More than scientifically intriguing, this unconventional and unexpected ferromagnetism pave the way for innovation products and novel nanotechnological applications, gathering the magnetism to interesting functionalities of these nanomaterials. Here, we investigate the non-conventional ferromagnetism observed at high temperatures in nanocrystalline cerium dioxide (CeO2or nanoceria) thin films that are optically transparent to visible light. Nanoceria exhibits several concrete applications in catalytic processes, photovoltaic cells, solid-state fuel cells, among others, which are mostly due to natural presence of oxygen vacancies and easy migration of the oxygen through the structure. The ferromagnetism in non-stoichiometric nanocrystaline ceria can be consistently described by ab initio electronic structure calculations, which support that oxygen vacancies cause the formation of magnetic moments and can provide a robust interconnectivity within magnetic polarons theoretical framework. Additionally, we present a conceptual model to account the oxygen transport to the non-conventional ferromagnetism at temperatures well above room temperature. The approach is complementary to the thermally-activated effective transfers of charge and spin around oxygen vacancy centers.

Tuning protein GlnB-Hs surface interaction with silicon: FTIR-ATR, AFM and XPS study.

Herbaspirillum seropedicae GlnB (GlnB-Hs) is a signal transduction protein involved in the control of nitrogen, carbon and energetic metabolism. The adsorption of GlnB-Hs deposited by spin coating on hydrophilic and hydrophobic silicon forms a thin layer that was characterized using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared attenuated total reflectance spectroscopy (FTIR-ATR). AFM allowed the identification of globular, face-up donut like array of protein on hydrophilic silicon substrate, favoring deprotonated residues to contact the silicon oxide surface. Over hydrophobic silicon, GlnB-Hs adopts a side-on conformation forming a filament network, avoiding the contact of protonated residues with silicon surface. XPS allowed us to determine the protonated and non-protonated states of nitrogen 1s (N 1s). The FTIR-ATR measurements provided information about protein secondary structure and its conservation, after surface adsorption.

Structure of ferromagnetic CrAs epilayers grown on GaAs(001).

Magnetic and structural properties of CrAs epilayers grown on GaAs(001) by molecular beam epitaxy have been studied. CrAs epilayers are orthorhombic for all thicknesses investigated but show a structural transition from a metastable phase for very thin films, to the usual bulk MnP-type orthorhombic phase at higher thicknesses. At intermediate thicknesses, there is a predominance of the new phase, although a contribution from the usual CrAs bulk phase remains clearly present. These results strongly suggest that the ferromagnetic signal measured at room temperature comes from the new metastable orthorhombic structure with an expanded b-axis induced by the substrate strain.