Room-temperature photomagnetism in the spinel ferrite (Mn,Zn,Fe)3O4 as seen via soft x-ray magnetic circular dichroism

We have used X-ray magnetic circular dichroism (XMCD) in conjunction with multiplet simulations to directly probe the origin of photomagnetism in nanocrystalline (Mn,Zn,Fe){sub 3}O{sub 4}. A photomagnetic effect at room temperature has been observed in these films with HeNe illumination. We have verified an intervalence charge transfer among octahedral Fe cations to account for the increase in magnetization observed at and above room temperature in small magnetic fields. Using XMCD, we demonstrate that the dichroism of Fe in octahedral sites increases by 18% at room temperature while the dichroism of Fe in tetrahedral sites does not change

Prevalence of Toll-like receptor signalling defects in apparently healthy children who developed invasive pneumococcal infection

Human primary immunodeficiencies affecting Toll-like receptor (TLR) signalling reveal a non-redundant role for TLR function in defense against pneumococcal infection. To determine the clinical relevance of TLR abnormalities, we studied a population predicted to be enriched for TLR defects-healthy children who had developed invasive pneumococcal infection in the absence of classic risk factors for infection. We describe the development and optimization of a peripheral blood TLR assay. By testing 38 healthy control neonates, children and adults we demonstrated that TLR function was stable over the first six decades of life. We tested 50 children with a history of invasive pneumococcal infection and although TLR defects were predicted to be over-represented in this population, we did not identify any TLR abnormalities. Although TLR signalling defects are associated with greatly enhanced susceptibility to invasive pneumococcal infection, our results suggest that routine clinical screening for TLR defects in healthy children who develop invasive pneumococcal infection is not justified

Structure, Magnetism, and Transport of CuCr2Se4 Thin Films

We report the successful growth of highly spin-polarized chalcogenide thin films of CuCr{sub 2}Se{sub 4}, which are promising candidates for spin-based electronic applications. We also present electronic structure calculations for CuCr{sub 2}Se{sub 4} that, together with magnetic and transport data, imply that the stoichiometric compound is a metallic ferromagnet with a relatively low density of hole-like carriers at the Fermi energy. These calculations also predict that a deficiency of Se will deplete the minority density of states at the Fermi energy perhaps leading to a half-metal. We have successfully grown thin films of CuCr{sub 2}Se{sub 4} by pulsed laser deposition on isostructural MgAl{sub 2}O{sub 4} substrates followed by an anneal in a Se-rich environment. X-ray diffraction confirms the structure of CuCr{sub 2}Se{sub 4} on MgAl{sub 2}O{sub 4} substrates as well as a secondary phase of Cr{sub 2}Se{sub 3}. X-ray absorption spectroscopy indicates that the chemical structure at the surface of the films is similar to that of bulk CuCr{sub 2}Se{sub 4} single crystals. Magnetization measurements indicate that these films saturate with a magnetic moment close to 5 {micro}{sub B} per formula unit and a T{sub c} above 400 K. X-ray magnetic circular dichroism shows that the magnetism persists to the surface of the film. Resistivity and Hall effect measurements are consistent with a p-type ferromagnetic metallic behavior and with the electronic structure calculations