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  • Springer  (263)
  • American Institute of Physics (AIP)  (81)
  • National Academy of Sciences  (8)
  • PANGAEA
  • 1995-1999  (352)
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  • 1
    Electronic Resource
    Electronic Resource
    Investigation of 90° coupling in Fe/Ag/Fe structures: "Loose spins'' and fluctuation mechanism (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 6432-6438 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Results are outlined of experimental work concerning Slonczewski's theories explaining 90° coupling: "loose spin'' theory and thickness-fluctuation mechanism. The loose spin theory suggests that 90° coupling originates from paramagnetic impurities in the interlayer of an exchange-coupled layered structure. The influence of these paramagnetic impurities on the magnetic exchange coupling was studied using the wedge technique. High-quality single-crystalline Fe/Ag/Fe samples were prepared in UHV and each sample consisted of two wedges: one wedge with additional Fe deliberately inserted during growth into the Ag interlayer and one wedge with a pure Fe/Ag/Fe structure. The detailed analysis of magneto-optic hysteresis loops revealed quantitatively the bilinearly and the 90° coupling strength. As predicted by loose spin theory additional Fe in the Ag spacer lead to a strong temperature dependence of the 90° coupling. According to the theory an increase of 90° coupling strength proportional to impurity concentration was detected while the strength of bilinear coupling decreased. For the pure Fe/Ag/Fe structure, a linear increase of the 90° coupling strength with decreasing temperature was observed. This result can be explained within the fluctuation mechanism which creates 90° coupling through a combination of interface roughness and intralayer ferromagnetic exchange. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359117
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  • 2
    Electronic Resource
    Electronic Resource
    Instrumentation for time-resolved electron diffraction spanning the time domain from microseconds to picoseconds (1998)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 2633-2643 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Recent instrumental improvements which successfully extend the time resolution of pulsed beam electron diffraction to the picosecond regime are described. Based on modifications of an existing nanosecond apparatus, a new sample inlet system, electron pulse generation laser, and amplified detector have been incorporated into the design such that significant improvements in both the signal level and ultimate time resolution are achieved; an upper estimate of the electron pulse width is ∼20 ps. Enhancements are such that, for operation in the nanosecond time domain, an entire diffraction pattern over a useful range of scattering angles may be collected from a gas-phase sample in a single electron pulse. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148991
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  • 3
    Electronic Resource
    Electronic Resource
    Microfabricated cantilever-based detector for molecular beam experiments (1998)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 3794-3797 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A low cost detector for particles in molecular beam experiments is presented which can easily be mounted in a molecular beam apparatus. The detector is based on microfabricated cantilevers, which can be employed either as single sensors or as sensor arrays. The single cantilever technique has been used to measure the absolute number of atoms coming out of a pulsed laser vaporization cluster source. The particles are detected by the shift of the thermally excited resonance frequency of the cantilever due to the cluster deposition. We have determined with the single cantilever the ratio of neutral to ionized clusters and we have investigated the cluster generation at different source conditions. In addition to this, a microfabricated cantilever array has been used to measure molecular beam profiles, which opens new possibilities for molecular beam deflection experiments. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149180
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  • 4
    Electronic Resource
    Electronic Resource
    Structural, field, and temperature dependence of noncollinear magnetic coupling in Fe/Cr(001) superlattices (abstract) : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 4782-4782 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.361670
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  • 5
    Electronic Resource
    Electronic Resource
    Thermal vacancy formation and positron–vacancy interaction in Ti3Al at high temperatures (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 724-728 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In order to study the formation of thermal vacancies in the Ti–Al alloy system, high-temperature positron lifetime measurements together with a modeling of defect formation in the framework of nearest-neighbor pair bonds were performed for α2Ti3Al and compared to recent results on γTiAl [U. Brossmann, R. Würschum, K. Badura, and H.-E. Schaefer, Phys. Rev. B 49, 6457 (1994)]. Substantial increases of the positron lifetime τ were observed for Ti65.6Al34.4 and Ti77.1Al22.9 in the temperature range T(approximately-greater-than)1200 K where thermal vacancy concentrations above the detection limit of positron annihilation are expected from the model calculations for the α2 phase. Within the high-temperature increase of the positron lifetime in the α2 and the β phase single-component positron lifetime spectra were observed. This behavior is in contrast to the two-component spectra observed conventionally at intermediate positron trapping rates and is attributed to a fast detrapping and retrapping of positrons at vacancies due to a low positron–vacancy binding energy. For this case, a vacancy formation enthalpy of HFV=(1.55±0.2) eV in α2Ti65.6Al34.4 and HFV=(1.8±0.2) eV in βTi77.1Al22.9 can be derived. These results are discussed in the context of recent 44Ti tracer diffusion studies. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362880
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  • 6
    Electronic Resource
    Electronic Resource
    Magnetism and microstructure of nanocrystalline nickel : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 5143-5145 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In order to study the influence of the nanocrystalline microstructure on the magnetic properties of pure nanocrystalline metals, in situ magnetic measurements of high-purity nanocrystalline nickel, prepared by a gas-condensation technique with subsequent compaction at various pressures have been performed. The approach to ferromagnetic saturation indicates free volumes in the nanocrystalline system of the size of individual missing crystallites as well as internal stresses. While the saturation polarization of the nanocrystalline Ni samples appears to be unchanged compared to coarse-grained Ni the coercive field and magnetic domains are strongly influenced by the nanocrystalline structure. The shape of the domains with sizes of 10–200 μm much larger than the crystallite size depends on the annealing state of the specimen. The initial coercive field increases with the compaction pressure during preparation. Upon annealing it further increases to a maximum value at Ta=500 °C and decreases at higher annealing temperatures. Additionally, the effect of oxygen located in the grain boundaries has been studied. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361535
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  • 7
    Electronic Resource
    Electronic Resource
    Factors affecting performance of NiO biased giant magnetoresistance structures : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 6234-6236 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have made spin-valve structures of Permalloy/Cu/Co by sputtering or electron-beam deposition onto the antiferromagnetic oxide NiO. The oxides were made either by deposition of the metals and subsequent oxidation or by growing them in situ using reactive sputtering. The magnetic properties of the giant magnetoresistance structures were studied by magnetoresistance, vibrating sample magnetometry, and ferromagnetic resonance methods. The oxides were characterized by x-ray diffraction and atomic force microscopy. We studied surface roughness and structure as functions of thickness and oxidation temperature and correlated the oxide properties with the magnetic performance. We found that the metal layer roughened during the postdeposition oxidation process and that the resulting oxide layers were very effective in pinning the direction of the magnetic moment of adjacent metal films. Coercive fields over 500 Oe were obtained for Co overlayers on NiO films but the exchange bias field was generally less than 100 Oe and was not strongly dependent on the roughness. The beneficial effects of this strong pinning were offset to some degree by higher switching fields required in spin-valve structures deposited over the Co. We also made reactively sputtered oxide antiferromagnetic films which had smoother surfaces than those made by postdeposition oxidation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362079
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  • 8
    Electronic Resource
    Electronic Resource
    Investigation of the high-field conductivity and dielectric strength of nitrogen containing polycrystalline diamond films (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 6332-6337 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The influence of nitrogen doping on the electrical properties of polycrystalline diamond films has been studied. The films were prepared in a microwave plasma chemical vapor deposition process using a H2/CH4/N2 gas mixture. The CH4 concentration was held constant at 0.5% and the nitrogen to carbon atomic ratio was varied between 0.01 and 0.2. The phase purities, surface morphologies, and the nitrogen contents of the films were analyzed by Raman spectroscopy, scanning electron microscopy, and secondary-ion mass spectroscopy, respectively. From current-voltage characteristics at field strengths up to 106 V cm−1 and in the temperature range between 300 and 800 K the conductivity was determined. The dielectric strength was obtained from the breakdown voltage measured using a voltage ramping rate between 50 and 100 V s−1. A minimum in high field and high-temperature conductivity and a maximum in dielectric strength was found for the samples prepared with a nitrogen to carbon atomic ratio of 0.02. Compared with nitrogen free samples the conductivity is lowered by more than three orders of magnitude and the dielectric strength is enhanced by a factor of two. The results will be discussed in terms of compensation of acceptor states by nitrogen donors and structural changes of the films. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359103
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  • 9
    Electronic Resource
    Electronic Resource
    Thermostability of Sm2(FeGa)17Cy prepared by gas-solid reaction (GSR) : The 41st annual conference on magnetism and magnetic materials (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 4539-4541 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The gas-solid-reaction (GSR) was used to introduce interstitial carbon atoms into Sm2Fe17−xGax compounds with x=0, 0.5, 1, and 2. For this process, powders made from homogenized ingots were annealed at 500 °C under methane for different times. The thermostability increases for small amounts of Ga and the investigation shows that Sm2Fe16.5Ga0.5Cy is stable up to 750 °C. In the case of Sm2Fe15Ga2Cy carburized for 6 h (y=2.0) and 18 h (y=2.2), the x-ray diffraction patterns show the Th2Zn17-type structure only. After annealing at 800 °C for 20 min the 6 h carburized sample shows a small amount of α-Fe and other phases and there is a large Fe content after annealing at 850 °C. For an 18 h carburized sample, less Fe and no other phases have be seen after annealing at 800 °C, i.e., the material is nearly single phase. The result that longer carburization times stabilize the Th2Zn17-type structure could also be manifested by Kerr microscopy. A comparison with mechanically alloyed Sm2Fe15Ga2C2 powders prepared with Sm excess shows that those are very stable up to 900 °C. The density of fine-grained Sm2Fe17−xGaxCy could be increased by hot pressing, but the degree of compaction and the phase purity very sensitively depend on the Ga content. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.365542
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  • 10
    Electronic Resource
    Electronic Resource
    High-temperature properties of GaInAs/AlGaAs lasers with improved carrier confinement by short-period superlattice quantum well barriers (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 2863-2865 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The influence of the carrier confinement on the output characteristics of GaInAs/AlGaAs lasers was investigated. To improve the carrier confinement, AlGaAs/GaAs short-period superlattices were used as quantum well barriers. In comparison to lasers with GaAs barriers the structures with the modified barriers show improved temperature properties at low threshold current densities without deterioration of the internal quantum efficiency (〉95%). High characteristic temperatures (T0) well above 300 K were measured between 20 and 75 °C and laser operation up to 238 °C could be achieved. The large improvement in T0 is mainly attributed to the reduced thermionic emission of carriers out of the quantum well due to the increased barrier height and the carrier reflection above the barrier by the short-period superlattice. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122611
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