Direct observation of magnetic contrast obtained by photoemission electron microscopy with deep ultra-violet laser excitation.

Magnetic circular dichroism (MCD) and magnetic linear dichroism (MLD) have been investigated in a photoemission electron microscopy (PEEM) system excited by a deep ultra-violet (DUV) laser (with λ = 177.3 nm and hυ = 7.0 eV) for the first time. High resolution PEEM magnetic images (down to 43.2 nm) were directly obtained on a (001)-oriented magnetic FePt film surface with a circularly-polarized light under normal incidence. Furthermore, a stepped Cr seeding layer was applied to induce the formation of large-area epitaxial FePt films with (001) and (111) two orientations, where MLD with large asymmetry was observed in the transition area of two phases. It demonstrates that DUV laser can be a powerful source for high resolution magnetic imaging in the laboratory in absence of synchrotron facilities.

Direct observation of the topological spin configurations mediated by the substitution of rare-earth element Y in MnNiGa alloy.

The evolution of topological magnetic domains microscopically correlates the dynamic behavior of memory units in spintronic application. Nanometric bubbles with variation of spin configurations have been directly observed in a centrosymmetric hexagonal magnet (Mn0.5Ni0.5)65(Ga1-yYy)35 (y = 0.01) using Lorentz transmission electron microscopy. Magnetic bubbles instead of biskyrmions are generated due to the enhancement of quality factor Q caused by the substitution of rare-earth element Y. Furthermore, the bubble density and diversified spin configurations are systematically manipulated via combining the electric current with perpendicular magnetic fields. The magnetic bubble lattice at zero field is achieved after the optimized manipulation.

Oxygen defect engineering by the current effect assisted with temperature cycling in a perovskite-type La0.7Sr0.3CoO3 film.

Introducing and modulating the oxygen deficiency concentration have been received as an effective way to obtain high catalytic activity in perovskite oxides. However, it is difficult to control the oxygen vacancy in conventional oxygen defect engineering due to harsh reaction conditions at elevated temperatures and the reducing atmosphere, which make it impractical for many technological applications. Herein, we report a new approach to oxygen defect engineering based on the combination of the current effect and temperature cycling at low temperature. Our investigations revealed that the electrical conductivity of the (011)-La0.7Sr0.3CoO3/PMN-PT film changes continuously from metallicity to insulativity under repeated transport measurements below room temperature, which indicates the transformation of the Co4+ state to Co3+ in the film. Further experiments and analysis revealed that oxygen vacancies can be well regulated by the combined current effect and temperature cycling in repeated measurements, which results in a decrease of Co4+/Co3+ and thus the remarkable variation of conductive properties of the film. Our work provides a simple and highly efficient method to engineer oxygen vacancies in perovskite-type oxides and brings new opportunities in designing high-efficiency oxidation catalysts.

New Fluoride-arsenide Diluted Magnetic Semiconductor (Ba,K)F(Zn,Mn)As with Independent Spin and Charge Doping.

We report the discovery of a new fluoride-arsenide bulk diluted magnetic semiconductor (Ba,K)F(Zn,Mn)As with the tetragonal ZrCuSiAs-type structure which is identical to that of the "1111" iron-based superconductors. The joint hole doping via (Ba,K) substitution &spin doping via (Zn,Mn) substitution results in ferromagnetic order with Curie temperature up to 30 K and demonstrates that the ferromagnetic interactions between the localized spins are mediated by the carriers. Muon spin relaxation measurements confirm the intrinsic nature of the long range magnetic order in the entire volume in the ferromagnetic phase. This is the first time that a diluted magnetic semiconductor with decoupled spin and charge doping is achieved in a fluoride compound. Comparing to the isostructure oxide counterpart of LaOZnSb, the fluoride DMS (Ba,K)F(Zn,Mn)As shows much improved semiconductive behavior that would be benefit for further application developments.

Visible-light-accelerated oxygen vacancy migration in strontium titanate.

Strontium titanate is a model transition metal oxide that exhibits versatile properties of special interest for both fundamental and applied researches. There is evidence that most of the attractive properties of SrTiO3 are closely associated with oxygen vacancies. Tuning the kinetics of oxygen vacancies is then highly desired. Here we reported on a dramatic tuning of the electro-migration of oxygen vacancies by visible light illumination. It is found that, through depressing activation energy for vacancy diffusion, light illumination remarkably accelerates oxygen vacancies even at room temperature. This effect provides a feasible approach towards the modulation of the anionic processes. The principle proved here can be extended to other perovskite oxides, finding a wide application in oxide electronics.

The physical mechanism of magnetic field controlled magnetocaloric effect and magnetoresistance in bulk PrGa compound.

The PrGa compound shows excellent performance on the magnetocaloric effect (MCE) and magnetoresistance (MR). The physical mechanism of MCE and MR in PrGa compound was investigated and elaborated in detail on the basis of magnetic measurement, heat capacity measurement and neutron powder diffraction (NPD) experiment. New types of magnetic structure and magnetic transition are found. The results of the NPD along with the saturation magnetic moment (MS) and magnetic entropy (SM) indicate that the magnetic moments are randomly distributed within the equivalent conical surface in the ferromagnetic (FM) temperature range. PrGa compound undergoes an FM to FM transition and an FM to paramagnetic (PM) transition as temperature increases. The magnetizing process was discussed in detail and the physical mechanism of the magnetic field controlled magnetocaloric effect (MCE) and the magnetoresistance (MR) was studied. The formation of the plateau on MCE curve was explained and MR was calculated in detail on the basis of the magnetic structure and the analysis of the magnetizing process. The experimental results are in excellent agreement with the calculations. Finally, the expression of MR = ß(T)X(2) and its application conditions were discussed, where X is M(H)/Meff, and Meff is the paramagnetic effective moment.

Visible-light-enhanced gating effect at the LaAlO3/SrTiO3 interface.

Electrostatic gating field and light illumination are two widely used stimuli for semiconductor devices. Via capacitive effect, a gate field modifies the carrier density of the devices, while illumination generates extra carriers by exciting trapped electrons. Here we report an unusual illumination-enhanced gating effect in a two-dimensional electron gas at the LaAlO3/SrTiO3 interface, which has been the focus of emergent phenomena exploration. We find that light illumination decreases, rather than increases, the carrier density of the gas when the interface is negatively gated through the SrTiO3 layer, and the density drop can be 20 times as large as that caused by the conventional capacitive effect. This effect is further found to stem from an illumination-accelerated interface polarization, an originally extremely slow process. This unusual effect provides a promising controlling of the correlated oxide electronics in which a much larger gating capacity is demanding due to their intrinsic larger carrier density.

Anomalous magnetism in strained La(1-x)Sr(x)CoO3 epitaxial films (0 ≤ x ≤ 0.5).

Spin state controlling has always been a focus of intensive studies due to its importance for novel effect exploration and information technology. Complex oxides with competitive mechanisms are suitable objects of study for this purpose due to their susceptibility to external stimuli. Perovskite cobaltate La(1-x)Sr(x)CoO3 is one of such oxides. Combined effects of lattice strains and hole-doping have been studied for the LSCO films with 0 ≤ x ≤ 0.5. It is found that the lattice strain, either tensile or compressive, destabilizes the ferromagnetic (FM) state of the epitaxial films, leading to a nonmagnetic state that extensively exists in a doping window embedding deep into the range of the FM phase in bulk counterparts. Density functional theory calculations reveal a distinct spin state transition due to the combined effects of lattice distortion and hole-doping, explaining the unique magnetic behaviors of LSCO.

Evolution of conduction channel and its effect on resistance switching for Au-WO3-x-Au devices.

We performed a systematic investigation on the dynamic behavior of conduction filaments (CFs) in WO3-x-based devices. It was found that the electric forming produced an electric structure consisted of a conductive channel (virtual cathode) started from cathode and an insulating band surrounding anode. Both the virtual cathode and the insulating region varied with repeated resistance switching. Set/reset operation affected device resistance mainly by modifying the CF, which formed in the setting process together with an insulating halo that separated it from the virtual cathode. The device resistance exhibited a sudden change exactly corresponding to the emergence/vanishing of the CF and a smooth variation corresponding to the outward/inward expansion/contraction of the insulating halo. Anode ablation occurred after repeated cycling, and it is the key factor affecting the endurance of device.

Gradual electroforming and memristive switching in Pt/CuO(x)/Si/Pt systems.

We report a memristive switching effect in Pt/CuOx/Si/Pt devices prepared by the rf sputtering technique at room temperature. Differently from other Cu-based metal filament switching systems, a gradual electroforming process, marked by a gradual increase of the device resistance and a gradual decrease of the device capacitance, was observed in the current-voltage and capacitance characteristics. After the gradual electroforming, the devices show a uniform memristive switching behavior. By Auger electron spectroscopy analysis, a model based on the thickness change of the SiOx layer at the CuOx/Si interface and Cu ion migration is proposed for the gradual electroforming and uniform memristive switching, respectively. This work should be meaningful for the preparation of forming-free and homogeneous memristive devices.

A high-mobility two-dimensional electron gas at the spinel/perovskite interface of γ-Al2O3/SrTiO3.

The discovery of two-dimensional electron gases at the heterointerface between two insulating perovskite-type oxides, such as LaAlO(3) and SrTiO(3), provides opportunities for a new generation of all-oxide electronic devices. Key challenges remain for achieving interfacial electron mobilities much beyond the current value of approximately 1,000 cm(2) V(-1) s(-1) (at low temperatures). Here we create a new type of two-dimensional electron gas at the heterointerface between SrTiO(3) and a spinel γ-Al(2)O(3) epitaxial film with compatible oxygen ions sublattices. Electron mobilities more than one order of magnitude higher than those of hitherto-investigated perovskite-type interfaces are obtained. The spinel/perovskite two-dimensional electron gas, where the two-dimensional conduction character is revealed by quantum magnetoresistance oscillations, is found to result from interface-stabilized oxygen vacancies confined within a layer of 0.9 nm in proximity to the interface. Our findings pave the way for studies of mesoscopic physics with complex oxides and design of high-mobility all-oxide electronic devices.

Large anisotropy in colossal magnetoresistance of charge orbital ordered epitaxial Sm(0.5)Ca(0.5)MnO(3) films.

We investigated the structure and magnetotransport properties of Sm(0.5)Ca(0.5)MnO(3) (SCMO) films epitaxially grown on (011)-oriented SrTiO(3) substrates, which exhibited clear charge/orbital ordering transition. A significant anisotropy of ∼1000 in the colossal magnetoresistance (CMR) effect was observed in the films with a thickness between 50 and 80 nm, which was distinctly different from the basically isotropic CMR effect in bulk SCMO. The large anisotropy in the CMR can be ascribed to the intrinsic asymmetric strain in the film, which plays an important role in tuning the spin-orbit coupling in manganite films. The origin of the peculiar CMR effect is discussed.

Phase coexistence and metastability in polycrystalline Pr(0.2)La(0.8)Fe(11.4)Al(1.6) compound.

Electrical resistivity, dc magnetization, ac magnetic susceptibility, and magnetic relaxation studies of polycrystalline Pr(0.2)La(0.8)Fe(11.4)Al(1.6) compound have been carried out. On the basis of the measurements of isofield magnetization and ac magnetic susceptibility, we provide evidence for phase coexistence (the appearance of the ferromagnetic phase in the antiferromagnetic matrix) rather than a spin glass, resulting in a cusp observed at ∼70 K in the zero-field-cooled thermal magnetization curve under low fields. The ferromagnetic clusters or nuclei appear randomly in the antiferromagnetic matrix according to the electrical resistivity results. An excellent magnetic-resistive correspondence is observed under medium fields. Under these fields large relaxation effects are presented in the vicinity of the phase transition temperature. Nonuniform variation of the relaxation rate with temperature gives a clear picture of the nucleation and growth of phases. Distinct metastable behavior is shown during the phase transition, which brings about the step-like behavior in the various magnetization curves.

[Studies on the recurrent attacks of acute adenolymphangitis due to Malayan filariasis].

OBJECTIVE: To explore the role of filarial and bacterial infections in the recurrent attacks of acute adenolymphangitis due to malayan fialriasis. METHODS: 1. To observe the seasonal fluctuation of acute attacks by performing monthly follow-up on patients with history of acute attacks in recent years. 2. To study the relationship between bacterial infection and filarial adenolymphangitis by performing bacteria culture and anti-streptolysin O test. 3. To investigate the variation of acute attacks by controlling filariasis transmission or by treating patients with a history of recurrent acute attacks. RESULTS: 1. The peak of acute attacks in patients coincided with the peak of vector transmission season. 2. Of the 97 cases examined by bacteria culture, 90 cases were negative; of the 255 cases examined by anti-streptolysin O test, the titres in 94.1% (143/152) of the cases with first attack and simple adenolymphangitis were within normal limits, however, the titres in 27.2% (28/103) of the cases complicated with elephantiasis were increased. 3. The acute attack rate of adenolymphangitis per year reduced significantly in cases with first attack and simple adenolymphangitis after effective control of filariasis transmission. 4. There was no evidence of the reduction of acute attacks by treating patients with DEC alone. CONCLUSION: In malayan filariasis endemic areas, the main causes of recurrent attacks of acute adenolymphangitis might be the repeated filarial infections due to the persistence of filariasis transmission.

Tegument changes of Schistosoma japonicum and Schistosoma mansoni in mice treated with artemether.

AIM: To study the effect of artemether (Art) on the tegument of schistosomes. METHODS: Mice infected with S japonicum cercariae for 7 and 35 d, or with S mansoni cercariae for 49 d were treated intragastrically with Art 200-300 mg.kg-1.d-1 for 2 d. Schistosomes were collected in groups of 2 mice at various intervals after medication for scanning electron microscopic observation. RESULTS: The tegumental changes induced by Art appeared to be similar in S japonicum and S mansoni: swelling and fusion of tegumental surfaces, vesicle formation and collapse of discoid-like sensory structures. In S japonicum the emergence of tegumental alterations was earlier in 7-d-old schistosomulae than that in 35-d-old adult worms. CONCLUSION: Art injured the teguments of S japonicum and S mansoni.

Scanning electron microscope observation on tegumental damage of 21-d-old Schistosoma japonicum induced by praziquantel.

AIM: To study the effect of praziquantel (Pra) on the tegument of 21-d-old schistosomula, mice infected with Schistosoma japonicum cercariae for 21 d were treated ig with Pra at a single dose. METHOD: Groups of mice were killed at different intervals within 48 h, and the worms were collected by perfusion for scanning electron microscopic observation. RESULTS: When the dose used was 300 mg.kg(-1), the worms showed mild or moderate swelling, fusion or even erosion and collapsed of the tegumental ridges, which was characterized by swelling of the discoid sensory structures. At higher dose of 500 mg.kg(-1), similar alterations in the worm surface were seen, but more extensive and serious. When Pra 500 mg.kg(-1) was given daily for 3 d, severe swelling, erosion and peeling of the tegument accompanied by the attachment of the host leukocytes on the damaged surface were seen. CONCLUSION: Pra exhibited a direct killing effect on 21-d-old schistosomula.

Effects of benzimidazole compounds on mice infected with secondary cysts of Echinococcus granulosus.

The effects of mebendazole (Meb), albendazole (Alb) and albendazole sulfoxide (AlbSO) on metacestodes of Echinococcus granulosus have been studied. The results show that Meb and Alb exhibit less effect on protoscoleces in vitro, but in vivo the protoscolicidal effect of Meb is higher than that of Alb. Both Meb and Alb are efficacious in the treatment of mice infected with secondary cysts of E. granulosus. In terms of the minimal effective dose required, the occurrence of collapsed and shrunk cysts after treatment, the drug-induced damage on the germinal layer and the relationship between the drug content in the cyst wall and the damage of germinal layer, the effect of Meb on metacestodes of E. granulosus is higher than that of Alb. The results also indicated that lower drug absorption rate and thickening of the adventitia during longer disease course are the two major factors affecting the efficacy of Meb and Alb, hence suggesting that increase of Meb absorption may be expected to raise the therapeutic effect of the drug. Finally, Alb is not only metabolized to AlbSo and AlbSP in vivo, but also metabolized by the cysts exposed to Alb in vitro. Experimental chemotherapy showed that AlbSO is the major effective metabolite of Alb, and its curative dose is only one half of the parent compound.

[Scanning electron microscopic study on the influence of monoclonal antibody on the invasion of macrophage by Leishmania parasites].

The interaction of promastigotes of Leishmania with mouse peritoneal macrophage in vitro was studied by scanning electron microscopy. The results showed that when promastigotes had been incubated with 1/1,000 McAb for 1 h, morphological changes could be seen in most promastigotes, some promastigotes were lysed and some promastigotes although adhered to the macrophage, but no penetration could be seen. When 1/1,000 McAb had been inactivated at 56 degrees C for 1 h and then incubated with promastigotes, scanning electron microscopic examination showed the promastigotes closely adhered to the surface of macrophage with their anterior end "buried" within macrophage. The results of the present study suggested that the mechanism of promastigote-macrophage adhesion was ligand-receptor binding interaction (Figs. 1-11).

[Screening antihydatid drugs using cultivated germinal cells of Echinococcus granulosus].

Germinal cells isolated from Echinococcus granulosus cysts harbored in mice have been maintained in an in vitro culture system containing RPMI 1640 supplemented by 20% calf serum, and used as a model for screening anti-hydatid drugs. When the germinal cells were maintained in the medium for 6 days, the cell proliferation rate was rather high in the first four days but declined in the last two days. In screening drugs, 1.4 x 10(6) germinal cells were exposed to known effective drugs against metacestodes of E. granulosus in mice, such as mebendazole (Meb), albendazole (Alb) or praziquantel (Pra) at various concentrations. One to three days after exposure, cell counts were made daily in 3 samples of each drug concentration. The mean cell number of each group was compared with that of the control and the inhibition rate of the cell was then calculated. The results showed that the minimal effective concentrations of Meb, Alb and Pra, were 1.0 (48 h), 2.5 (24 h) and 10.0 (72 h) micrograms/ml, respectively, while the inhibition rates of the cell were 34.1, 55.7 and 18.5%. Interestingly, the in vitro effects of Meb, Alb and Pra were consistent to those obtained from the in vivo tests, ie Meb > Alb > Pra. Nevertheless, after exposure of germinal cells to Meb at 2.5 micrograms/ml for 24 h, the cells appeared in roughness, indistinction, shrunk or swelling, collapse, deformation and hole-like feature detected by light microscopy and scanning electron-microscopy, while the ultrastructure alterations of the cells noted by transmission electron-microscopy were lysis in cytoplasm, disruption or disappearance of nucleus and even darkness of the whole cell.(ABSTRACT TRUNCATED AT 250 WORDS)