RESUMO
Room temperature ferromagnetism has been observed in the Cu doped ZnO films deposited under an oxygen partial pressure of 10-3 and 10-5 torr on Pt (200 nm)/Ti (45 nm)/Si (001) substrates using pulsed laser deposition. Due to the deposition at relatively high temperature (873 K), Cu and Ti atoms diffuse to the surface and interface, which significantly affects the magnetic properties. Depth sensitive polarized neutron reflectometry method provides the details of the composition and magnetization profiles and shows that an accumulation of Cu on the surface leads to an increase in the magnetization near the surface. Our results reveal that the presence of the copper at Zn sites induces ferromagnetism at room temperature, confirming intrinsic ferromagnetism.
RESUMO
Here we present a study of magnetism in Co_{0.05}Ti_{0.95}O_{2-δ} anatase films grown by pulsed laser deposition under a variety of oxygen partial pressures and deposition rates. Energy-dispersive spectrometry and transmission electron microscopy analyses indicate that a high deposition rate leads to a homogeneous microstructure, while a very low rate or postannealing results in cobalt clustering. Depth resolved low-energy muon spin rotation experiments show that films grown at a low oxygen partial pressure (≈10^{-6} torr) with a uniform structure are fully magnetic, indicating intrinsic ferromagnetism. First principles calculations identify the beneficial role of low oxygen partial pressure in the realization of uniform carrier-mediated ferromagnetism. This work demonstrates that Co:TiO_{2} is an intrinsic diluted magnetic semiconductor.
RESUMO
A subclone of a human B lymphoblastoid cell line, CESS-2, spontaneously secreted a kind of BCDF (B-BCDF) in their culture supernatant without any stimulation. B-BCDF induced IgG and IgM secretions in human B lymphoblastoid cell lines, CESS cells and CL-4 cells, respectively. BCDF-responsive CESS cells expressed IgG on their surface, whereas CESS-2, which were able to secrete B-BCDF, did not express surface IgG. B-BCDF could induce Ig-secretion in SAC-stimulated low density peripheral B cells, but did not induce Ig secretion in nonstimulated B cells. B-BCDF did not show any IL 2, BCGF, or gamma-interferon activities. B-BCDF was highly purified by gel filtration on an AcA-34 column, by chromatofocusing and ion exchange chromatography on an HPLC system, and by gel filtration on an HPLC column. Highly purified preparations showed a single protein band in SDS-PAGE analysis. The m.w. and isoelectric points of the factor were 20,000 and pH 5.1 to 5.2, respectively. The minimum protein amount required for Ig induction in B cell lines was 16 ng/ml.