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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 6460-6462 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of adding Cl impurity on the long-range antiferromagnetic coupling in [ZnTe|MnTe] magnetic semiconductor superlattices has been investigated by neutron diffraction. Superlattices consisting of five atomic planes of ZnTe alternated with ten atomic planes of MnTe[(ZnTe)5|(MnTe)10] have been prepared by molecular-beam epitaxy both with and without Cl added to the MnTe and/or ZnTe layers during deposition. This was motivated by the fact that Cl can form either shallow or deep donor levels in II–VI semiconductors, and that such electronic states can serve to modify magnetic interlayer exchange. Unchlorinated samples showed magnetic correlation lengths of around 225 Å ((approximate)5 bilayers) at low temperatures, and the addition of Cl increased the correlation length at 15 K by nearly a factor of 2 to approximately 450 Å. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 5813-5815 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Low-angle inelastic neutron scattering was used to study the temperature and wave vector dependence of the spin waves in La0.67Ca0.33MnO3 perovskite-based colossal magnetoresistance material. At low q the spin waves show Heisenberg ferromagnetic dispersion (E=Dq2+Δ) where D is the spin stiffness, q is the wave vector, and Δ is the energy gap. However, the temperature renormalization of the spin stiffness D is anomalous, and as T increases toward Tc, D does not show the expected power law collapse, but rather exhibits a sudden sharp drop suggestive of a first-order phase transition. Detailed neutron measurements of the order parameter in zero applied field showed a similar first-order-like transition. However, no temperature hysteresis was observed in either D or in the magnetization. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 5564-5566 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The spin dynamics of Nd0.6Sr0.4MnO3 have been determined along [qqq], [qq0], and [00q] propagation directions using inelastic neutron scattering. At T=13 K, the low-q Mn–Mn mode energies varied quadratically with wave vector q, but exhibited marked softening on approach to the zone boundaries when compared with a Heisenberg nearest-neighbor exchange calculation. At the larger q's the modes also show evidence of increasing spin wave energy width. The temperature dependence of the spin wave stiffness parameter D was measured up to Tc=273 K and showed conventional behavior. The 0 K value of D=150 meV Å2 yields D(0)/kTc=6.3. No anomalous E=0 central mode intensity was observed on approach to Tc. At low T additional modes were observed and are ascribed to Nd–Mn exchange interactions. These modes have q=0 spin wave gap of 2.1 meV compared to 1.1 meV for the Mn–Mn excitations.© 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetic coupling of the Fe layers in Fe/Si multilayers strongly depends on the morphology of the iron-silicide interlayer that forms during deposition. Antiferromagnetic interlayer coupling is only observed in Fe/Si multilayers with crystalline interlayers in the CsCl structure. Recently, it has been shown that single layers of Fe–Si in the CsCl structure can be grown epitaxially on Si over a range of stoichiometries. FeSi films are reported to be Kondo insulators below 50 K. We find evidence of a magnetic phase transition in antiferromagnetically coupled Fe/Si multilayers. Ms measured in a constant applied field of 50 kOe shows T3/2 behavior down to 10 K. However, M(T) at a lower constant field peaks around 50 K and decreases at lower temperature, indicating enhanced antiferromagnetic coupling or a phase transition. The remanent magnetization increases monotonically with decreasing temperature and has been explained by invoking thermally activated coupling. However, the saturation field also increases with decreasing temperature, indicating a stronger antiferromagnetic interaction. We explore the suggestion that the interlayer coupling is biquadratic in nature. Polarized neutron reflectometry has also been used to get a clearer picture of the complicated magnetic behavior of this multilayer system. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 4779-4781 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial (11¯02) Dy/Y rare earth superlattices and a thick (11¯02) Dy film, grown on sapphire with Y/Ta buffer layers, have been prepared by molecular beam epitaxy. Neutron diffraction and SQUID magnetization measurements on a single 200 nm thick (11¯02) Dy layer showed nearly bulk behavior. However, for the (11¯02) Dy/Y superlattices we found different magnetic behavior depending on the relative Dy to Y-layer thickness. The superlattices exhibit both ferromagnetic and helical phases, but with the Néel and Curie temperatures significantly different from bulk Dy. These results differ from previous findings in Dy/Y superlattices grown along [0001]. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Utilizing the magneto-optic Kerr effect (MOKE) in conjunction with x-ray and neutron reflectometry (NR) and diffraction, we have studied the magnetic coupling of Fe/Cr(001) superlattices grown at room temperature and 250 °C. Only the samples grown at elevated temperature exhibit noncollinear coupling of 5.0 nm Fe layers across 1.7 nm Cr interlayers. The noncollinear samples feature a less-disordered in-plane interfacial structure than those grown at room temperature. Using x-ray diffuse reflectivity, we have measured a length scale of 10 nm for these in-plane features. We have also observed, via NR, a remanent noncollinear coupling angle of 50° and, via MOKE and NR, a gradual approach to saturation at upwards of 7 kOe. These features can be explained qualitatively by the proximity magnetism model of Slonczewski. We will compare the predictions of both the proximity and bilinear/biquadratic models with our data and present the results of ongoing neutron measurements of the temperature dependence of the coupling. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 3765-3766 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using polarized-neutron reflectivity, we have measured the temperature dependence of the noncollinear magnetic coupling of ferromagnetic iron across chromium interlayers in two superlattice samples. The first sample, (52 Å Fe/17 Å Cr)9, exhibits a room temperature remanent magnetic structure consisting of successive Fe layer moments aligned at 50° relative to each other. This magnetic structure remains unchanged upon cooling the sample to 42 K. In contrast, a superlattice with a thicker Cr interlayer, [44 Å Fe/88 Å Cr]30, passes in a 20 K-wide transition centered on TN=240 K from a room temperature state with Fe moments aligned at 90° to an uncoupled state. The formation of the incommensurate Cr spin density wave state below TN suppresses the interlayer coupling. The thinner Cr interlayers do not undergo a transition to this bulk structure, hence exhibit no suppression of coupling. In both samples, the coupling strength decreases for temperatures at and above room temperature. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 7339-7341 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetic structure and dynamics in the colossal magnetoresistance (CMR) class perovskite La0.53Ca0.47MnO3 have been studied by elastic and inelastic neutron scattering. This composition is near the 0.5 Ca transition from a metallic ferromagnet to an insulating antiferromagnet. Powder neutron diffraction on these samples showed coexisting ferromagnetic and antiferromagnetic phases at low temperature and a splitting of the lattice parameters of the antiferromagnetic phase near TN, reflecting the onset of the charge ordered state. Inelastic scattering measurements of the ferromagnetic excitations exhibited well-defined spin waves of resolution width below Tc. The spin waves exhibited conventional Heisenberg behavior with dispersion of the form E=Dq2+Δ with spin stiffness D(T=0 K)(approximate)135 meV Å2 and an energy gap Δ(approximate)0.1 meV. The value of the spin wave stiffness D is similar to that found for other ferromagnetic perovskite materials, and it renormalized with temperature in a manner consistent with the magnetization. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 22 (1999), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Electrical conductance (λ) was measured continuously and in vivo on leaf surfaces of Vicia faba and Aegopodium podagraria. λ increased with rise and decreased with fall in humidity, exhibiting a hysteresis during an applied humidity cycle [90–20–-90% relative humidity (r.h.)]. After treatment with NaNO3 aerosols, a sudden increase in λ was observed at 73% r.h., which is close to the deliquescence point of the salt. Transpiration and electrical conductance of untreated leaves were measured simultaneously under conditions of constant r.h., while the photosynthetic photon flux density and CO2 concentration of the air were varied to induce changes of stomatal aperture. At 35% r.h., changes of light and CO2 level revealed a strong correlation between stomatal conductance (gS) and λ for Vicia faba leaves. This was also found at 90, 75, 60, 45 and 25% r.h. on the lower but not on the astomatous, upper surface of Aegopodium podagraria. The correlation between gS and λ for stomata-bearing leaf surfaces indicates that an equilibrium exists between the ambient water vapour phase and the liquid water phase on and within the cuticle. This is modified by transpired water vapour influencing the air humidity inside the boundary layer. Our results imply re-condensation of transpired water vapour to salts on the leaf surface and its sorption to the cuticle.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Aquaculture research 27 (1996), S. 0 
    ISSN: 1365-2109
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The objective of this study was to assess the efficacy and mode of action of 2-phenoxyethanol as an anaesthetic for two size classes of goldfish, Carassius auratus (L.), at three different temperatures. Goldfish (2.15 ± 0.05 g, and 9.19 ± 0.17 g) were exposed to 0.3, 0.4 and 0.5 ml 2-phenoxyethanol l1 at 20, 25, and 30oC. Time needed to induce anaesthesia was dependent on concentration and water temperature. At temperatures at and below 25oC, 0.4 ml l1 was needed to induce total loss of equilibrium within less than 15 min. Above 25oC, 0.5 ml l1 was required to induce anaesthesia. Recovery rate was independent of the length of anaesthesia, which indicates that the anaesthetic is taken up and lost via a concentration gradient at the gill membrane and skin/solution interface. Fish recovered within less than 10 min after they had been taken out of the anaesthetic solution. In a second experiment, goldfish responded to a repeated exposure to 2-phenoxyethanol daily over a period of 14 days with increased tolerance, which indicates a habituation response to the anaesthetic. The use of 2-phenoxyethanol as an anaesthetic both for short-term anaesthesia and for anaesthesia under transport conditions is discussed.
    Type of Medium: Electronic Resource
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