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  • 1
    Electronic Resource
    Electronic Resource
    Emergent excitations in a geometrically frustrated magnet (2002)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 418 (2002), S. 856-858 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Frustrated systems are ubiquitous, and they are interesting because their behaviour is difficult to predict; frustration can lead to macroscopic degeneracies and qualitatively new states of matter. Magnetic systems offer good examples in the form of spin lattices, where all interactions between ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature00964
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  • 2
    Electronic Resource
    Electronic Resource
    Optical and structural properties of strained InAlAs/InAsxP1−x multi-quantum wells grown by solid source molecular beam epitaxy (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 2622-2627 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on the optical and structural properties of strained InAlAs/InAsxP1−x heterostructures grown by solid source molecular beam epitaxy. The incorporation of As4 into strained InAsP has been studied using x-ray diffraction and photoluminscence measurements. We find that the incorporation of As decreases as x in the InAsxP1−x increases due, presumably, to increased strain. In addition, we have examined the effect of interface growth conditions and barrier material on the quantum well properties. The 4.2 K photoluminescence spectra of InAlAs/InAsP multi-quantum wells grown with different As and P flux switching conditions at the interfaces were compared with that of higher quality InP/InAsP multi-quantum wells. This comparison shows that the interface quality of InAlAs/InAsP multi-quantum wells is highly dependent on the switching conditions at the interfaces, especially the exposure time of InAsP surface to an As4 overpressure. This sensitivity is due to the As–P exchange reaction at the interfaces of InAlAs/InAsP. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371101
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  • 3
    Electronic Resource
    Electronic Resource
    Large room-temperature intergrain magnetoresistance in double perovskite SrFe1−x(Mo or Re)xO3 (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 1737-1739 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report significant intergrain magnetoresistance (IMR) in polycrystalline double perovskites of SrFe1−x(Mo or Re)xO3 at room temperature. Systematics of the temperature dependence of IMR indicates that the observed large room-temperature IMR in SrFe1/2Mo1/2O3 originates from the ferrimagnetic nature of insulating grain boundaries as well as the half-metallicity of this perovskite. Our results indicate that a new avenue for spin-polarized tunneling junctions is to utilize insulating interface layers with ferromagnetic or ferrimagnetic coupling. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.123672
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  • 4
    Electronic Resource
    Electronic Resource
    Structural and magnetic properties of CoFe alloy films : The 41st annual conference on magnetism and magnetic materials (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 4764-4766 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The investigation of the structural and magnetic properties of bcc Co1−xFex (0.1〈x〈0.4) alloy films prepared on MgO(001) substrates using e-beam evaporation and pulsed laser ablation deposition (PLAD) methods is reported. Both structural and magnetic properties seem to be strongly correlated to the deposition conditions, i.e., substrate temperatures (Ts) and deposition rates (DR). To identify the stability limits of the bcc structure in the phase diagram, our study is limited to the Co-rich compounds. For x≥0.3 at high Ts (500 °C), alloy films deposited by e-beam evaporation exhibit a bcc (001) growth, showing the magnetic anisotropy with easy axis parallel to the MgO [100] crystal axis. In the PLAD technique, the excellent bcc (001) film growth is observed at Ts=300 °C for x=0.25 which is close to the concentration limit of the bcc regime in the equilibrium bulk phase diagram, whereas the same compound films deposited at high Ts reveal the mixed phase of fcc (001) and bcc (001) structures. Magnetic hysteresis measurements of the film grown by the PLAD technique exhibit similar results to those of the films deposited by e-beam evaporation. These results show that, for the well-crystallized films with a bcc (001) texture, the magnetocrystalline anisotropy develops in-plane.© 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.365457
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  • 5
    Electronic Resource
    Electronic Resource
    Magnetic properties and magnetic phase diagram of frustrated Co1−xFexPt3 compounds : The 41st annual conference on magnetism and magnetic materials (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 5273-5275 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The investigation of the magnetic properties of the pseudobinary Co1−xFexPt3 L12 ordered compounds resulting from alloying ferromagnet CoPt3 and frustrated antiferromagnet FePt3 is reported. The magnetic phase diagram of this system shows the presence of a pure spin glass phase that separates the ferromagnetic region from the antiferromagnetic one. On the Co-rich side (x〈0.6), two re-entrant spin glass phases are found to emerge at low temperature in the ferromagnetic region. On the iron-rich side, an antiferromagnetic region with two antiferromagnetic [〈fraction SHAPE="CASE"〉12 〈fraction SHAPE="CASE"〉120] and [〈fraction SHAPE="CASE"〉1200] structures is observed for 1≥x≥0.8. This magnetic phase diagram is discussed comparatively with the previously determined (Fe–Mn)Pt3 and (Co–Mn)Pt3 phase diagrams. The randomness of the average exchange interaction is suggested to arise from a competition between the three dominant magnetic interactions JCoCo, JFeFe, and JCoFe of 3d atoms in sites of second nearest neighbors in the L12 structure. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.364456
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  • 6
    Electronic Resource
    Electronic Resource
    Calculation of CO2 laser beam absorptance as a function of temperature for steels by the numerical method (1995)
    Springer
    Journal of materials science 30 (1995), S. 784-792 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Temperature distributions were measured during the irradiation of a CO2 laser beam at one end of a rod-shaped specimen and at the centre of a thin plate-shaped specimen. Regarding the measured temperature distributions as one-dimensional and two-dimensional unsteady state heat transfer solutions, CO2 laser beam absorptances were calculated using a modified finite difference method. Temperature dependence of thermal properties, heat loss due to convection and latent heat during melting of the specimen were taken into account in this numerical calculation. Increasing the specimen temperature from room temperature to melting point, absorptances of STS304 stainless steel and SM45C steel were calculated as 8 ∼ 40% and 6 ∼ 41% for the one-dimensional calculation, and as 9.3 ∼ 41% and 5 ∼ 41% for the two-dimensional calculation, respectively. These calculated absortances were very close to theoretical values at relatively low temperature, which were calculated from the electrical resistivities of the specimens. Increasing the temperature of the specimens, absorptances increased considerably due to oxidation of the specimens. Regardless of specimen composition and specimen dimension, both absorptances showed nearly the same value of 41% at their melting points, in which the structures of both metals became amorphous phases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00356343
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  • 7
    Electronic Resource
    Electronic Resource
    Titanium nitride laser-beam surface-alloying treatment on carbon tool steel (1990)
    Springer
    Journal of materials science 25 (1990), S. 3583-3591 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract In order to improve the wear resistance of tool steel, a study of TiN surface-alloying treatment on 1% carbon steel by irradiation with a CO2 laser beam was performed. Argon and nitrogen were used as shielding gases, and their effects on the formation of the surface-alloyed layer were investigated. The effect of cobalt additions to the TiN powder on the hardness of the alloyed layer was also investigated. When argon was used as shielding gas, the depth of the alloyed layer was increased compared with the depth when nitrogen was used as a shielding gas. A portion of the TiN decomposed into titanium in the argon environment, the nitrogen apparently being lost as a gas. The structure of the surface-alloyed layer was composed of a ferritic phase without martensitic structure even at high cooling rates. When this layer was annealed at 1000 ° C for 3 h, part of the titanium precipitated as TiC particles. The hardness of the annealed alloyed layer increased to about 500 Hv. This increase in hardness was accompanied by the appearance of martensite. When nitrogen was used as shielding gas, decomposition of TiN was suppressed and the hardness of the alloyed layer reached 850 Hv. These layers had a martensitic structure. Thus, nitrogen is preferable to argon as a shielding gas if a martensitic structure is desired in this system. When 5% cobalt was added to the TiN powder, the hardness of the alloyed layer increased to 1100 Hv. This increased hardness is caused by stabilization of the martensitic structure caused by an increase in theM s temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00575393
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  • 8
    Electronic Resource
    Electronic Resource
    Suppression of θ″ formation in the SiC whisker-reinforced Al-4 wt% Cu composites (1992)
    Springer
    Journal of materials science 27 (1992), S. 2599-2605 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Precipitation characteristics in a powder metallurgy (Al-4wt% Cu)-SiC whisker composite were investigated using transmission electron microscopy, differential scanning calorimetry, and macrohardness measurement. The results of macrohardness measurement show that the peak ageing is significantly retarded in the SiC whisker-reinforced Al-Cu alloys. It is shown that the suppression of θ″ formation plays an important role in the retarded age hardening. The suppression of θ″ formation is attributed to a high density of dislocations due to the difference in the thermal contraction between the whiskers and matrix. Numerical analysis was performed to estimate the misfit strain generated during cooling near the whiskers. The results indicate that a high density of dislocations should be developed by the relief of the misfit strain.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00540675
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  • 9
    Electronic Resource
    Electronic Resource
    Chromium carbide laser-beam surface-alloying treatment on stainless steel (1992)
    Springer
    Journal of materials science 27 (1992), S. 2967-2973 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract In order to improve the resistance to wear, oxidation and corrosion of a stainless steel die, chromium carbide surface-alloying treatment was carried out on a 12 % Cr stainless steel using a CO2 laser. Cr3C2 powder slurry was coated on the stainless steel and then a 3 kW CO2 laser beam was used to irradiate the specimen. The thickness of surface-alloyed layer was about 0.3 mm and the chromium concentration was about 40 % throughout the alloyed-region. Large amounts of Cr3C2 and Cr7C3 were also distributed in this alloyed layer. From the results of the isothermal oxidation test at 960 °C for 100 h, it was found that the surface-alloying treatment improved the oxidation resistance by about 100 times due to the distribution of chromium carbides and the increase in the chromium concentration. The results of the cyclic oxidation test revealed that the oxidation layer was very stable on the chromium carbide surface-alloyed region, while it scaled off very easily from the substrate region due to porous oxidation products. The microhardness was about 1100 Hv due to the dispersion and precipitation of chromium carbides in addition to the martensitic structure in the surface-alloyed region. The microhardness did not decrease much, despite heating at 960 °C for 100 h. The chromium carbide surface-alloying treatment improved the wear-resistance greatly, and the results of the wear-resistance test were very consistent with those of the microhardness test.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01154107
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  • 10
    Electronic Resource
    Electronic Resource
    Amino acid content in xylem sap of regrowing alfalfa (Medicago sativa L.): Relations with N uptake, N2 fixation and N remobilization (1993)
    Springer
    Plant and soil 149 (1993), S. 167-174 
    Details
    ISSN: 1573-5036
    Keywords: asparagine ; aspartate ; free-amino acids ; Medicago sativa ; 15N labelling ; nitrogen remobilization ; regrowth ; xylem sap
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract During vegetative regrowth of Medicago sativa L., soil N, symbiotically fixed N2 and N reserves meet the nitrogen requirements for shoot regrowth. Experiments with nodulated or non-nodulated plants were carried out to investigate the changes in N flows originating from the different N sources and in xylem transport of amino acids during regrowth. Exogenous N uptake, N2 fixation and endogenous N remobilization were estimated by 15N labelling and amino acids in xylem sap were analysed. Removal of shoots resulted in great declines of exogenous N flows derived either from N2 or from NH4NO3 during the first week of regrowth, thereafter recovery increased linearly. Mineral N uptake as well as N2 fixation occurred mainly between the 10th and 18th day after removal of shoots while exogenous N assimilation in intact plants remained at a steady level. Nitrogen remobilization rates in defoliated plants increased by at least three to five-fold, especially during the first 10 days following shoot removal. Compared to control plants, contents of amino acids in xylem sap, during the first 10 days of regrowth, were reduced by about 72% and 82% in NH4NO3 grown and in N2 fixing plants, respectively. Asparagine was the main amino acid transported in xylem sap of both treated plants. Its relative contents during this period significantly decreased from 75% to 59% and from 67% to 36% respectively in non-nodulated plants and in nodulated ones. This decline was accompanied by compensatory increase in the relative contents of aspartate and glutamine.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00016606
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