Ferromagnetic interfacial interaction and the proximity effect in a Co2FeAl/(Ga,Mn)As bilayer.

The magnetic properties of a Co2FeAl/(Ga,Mn)As bilayer epitaxied on GaAs (001) are studied both experimentally and theoretically. Unlike the common antiferromagnetic interfacial interaction existing in most ferromagnet-magnetic semiconductor bilayers, a ferromagnetic interfacial interaction in the Co2FeAl/(Ga,Mn)As bilayer is observed from measurements of magnetic hysteresis and x-ray magnetic circular dichroism. The Mn ions in a 1.36 nm thick (Ga,Mn)As layer remain spin polarized up to 400 K due to the magnetic proximity effect. The minor loops of the Co2FeAl/(Ga,Mn)As bilayer shift with a small ferromagnetic interaction field of +24 Oe and -23 Oe at 15 K. The observed ferromagnetic interfacial coupling is supported by ab initio density functional calculations. These findings may provide a viable pathway for designing room-temperature semiconductor spintronic devices through magnetic proximity effect.

Temperature effect of the local structure in liquid Sb studied with x-ray absorption spectroscopy.

The temperature dependence of the local structure of liquid Sb has been studied by x-ray absorption spectroscopy. It is shown that about 10% of the atoms with coordination of 3 and weak Peierls distortion exist in liquid Sb just above its melting point. The Peierls distortion weakens gradually with increasing temperature and vanishes at about 750 degrees C. This structural variation in liquid Sb is different from the normal liquid-liquid phase transition. This work reveals the relationship between the variation in the local structure and the change in the physical properties, such as the electrical resisitvity of liquid Sb, with temperature. The complete agreement between the measured electrical resistivity values during heating and cooling processes suggests that the structural units with the features of a rhombohedron appear above the melting point of Sb during solidification.

Evidence of structural defect enhanced room-temperature ferromagnetism in Co-doped ZnO.

We report experimentally that room-temperature ferromagnetism of Co-doped ZnO is strongly correlated with structural defects, and that carriers involved in carrier-mediated exchange are by nature by-products of the creation of the defects. On the other hand, the carrier concentration has pronounced influences on the absorption edge in optical transmission spectra of epitaxial Co:ZnO films, in which both a blue-shift and a red-shift are observed. Furthermore, high-temperature annealing results in evolution of the local Co structure from Co(2+) replacing Zn(2+) to a Co(3)O(4)-based phase, which most likely accounts for the transition from ferromagnetism to paramagnetism in the Co:ZnO films.

Micronuclei in nasal mucosa, oral mucosa and lymphocytes in students exposed to formaldehyde vapor in anatomy class.

The frequency of micronuclei (MN) in cells of the nasal mucosa, oral mucosa and in lymphocytes was evaluated for 25 students in anatomy classes exposed to formaldehyde (FA) over an 8-week period. Each student served as his or her own control. The time-weighted average concentration (TWA) of formaldehyde in anatomical laboratories and in students' dormitories was 0.508 +/- 0.299 mg/m3 and 0.012 +/- 0.0025 mg/m3, respectively. A higher frequency of micronuclei was observed in nasal and oral exfoliative cells after formaldehyde exposure (3.85 +/- 1.48 vs 1.20 +/- 0.676 and 0.857 +/- 0.558 vs 0.568 +/- 0.317, paired-t test: P < 0.001 and P < 0.01, respectively). No significant increase in the frequency of lymphocyte micronuclei was found after formaldehyde exposure (P > 0.05). The present study shows that nasal mucosa cells exposed through respiration are the chief target of FA-induced genotoxic effects.

Lymphocyte subsets and sister-chromatid exchanges in the students exposed to formaldehyde vapor.

The present report evaluates the effects of formaldehyde (FA) exposure on peripheral lymphocytes by using both genetic and immunological parameters. Twenty-three non-smoking students in the study had inhalation exposure to 0.508 +/- 0.299 mg/m3 of FA for a period of 8 weeks (3h x 3 times each week) during anatomy classes. As for composition of lymphocyte subsets after FA exposure, significant increase was found in the percentage of CD19 (B cells), while significant decrease was observed in CD3 (total T cells), CD4 (T helper-inducer cells), and CD8 (T cytotoxic-suppressor cells) with a P < 0.01. Increase in the ratio of T-helper-inducer cells to T-cytotoxic-suppressor cells (T4/T8) was also observed with statistical significance after exposure (P < 0.001). In the meanwhile, no significant difference (P > 0.05) was reported between lymphocyte proliferation rate and sister-chromatid exchange (SCE) at the exposure level and duration. It is suggested that the lymphocyte subsets may be most susceptible to the effects of FA, though a single immunological endpoint is rarely related with pathophysiological interpretation.

Tuning of uniaxial magnetic anisotropy in amorphous CoFeB films.

We demonstrate that the uniaxial magnetic anisotropy (UMA) of amorphous CoFeB films can be tuned by crystallinity and orbital moment ratio, combining the results of magnetization reversal and ferromagnetic resonance with high-resolution transmission electron microscopy, x-ray-absorption near-edge structure and x-ray magnetic circular dichroism. Isotropic polycrystalline buffers of tungsten (W), tantalum (Ta), and copper (Cu) between CoFeB and Si(100) substrates have direct and crucial bearing on the interfacial microstructure and orbital moment ratio. Compared with Ta and Cu buffer, CoFeB with W buffer exhibits obvious UMA and has lower crystallinity at the interface and higher orbital moment. Amorphous phase distributed homogeneously in CoFeB film grown on W buffer contributes to improve the easy-axis squareness with a sharp magnetization reversal. Our demonstrations not only realize effective tuning of UMA in amorphous CoFeB, but also provide an appealing alternative buffer (W) for CoFeB-based magnetic tunnel junctions.