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  • Articles: DFG German National Licenses  (75)
  • 1990-1994  (47)
  • 1985-1989  (28)
  • 1
    Electronic Resource
    Electronic Resource
    Granular giant magnetoresistive materials and their ferromagnetic resonances (abstract) : The 6th joint magnetism and magnetic materials (MMM)-intermag conference (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 6823-6823 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ferromagnetic resonance (FMR) can reveal important information on the size and shape of the ferromagnetic particles which are dispersed in granular giant magnetoresistive (GMR) materials. We have investigated the FMR spectra of three different types of granular GMR material, each with different properties: (1) melt-spun ribbons of Fe5Co15Cu80 and Co20Cu80, (2) thin films of Co20Cu80 produced by pulsed laser deposition, and (3) a granular multilayer film of [Cu(50 A(ring))/Fe(10 A(ring))]×50. We interpret the linewidth of these materials in as simple a manner as possible, as a "powder pattern'' of noninteracting ferromagnetic particles. The linewidth of the melt-spun ribbons is caused by a completely random distribution of crystalline anisotropy axes. The linewidth of these samples is strongly dependent upon the annealing temperature: the linewidth of the as-spun sample is 2.5 kOe (appropriate for single-domain particles) while the linewidth of a melt-spun sample annealed at 900 °C for 15 min is 3.8 kOe (appropriate for larger, multidomain particles). The linewidth of the granular multilayer is attributed to a restricted distribution of shape anisotropies, as expected from a discontinuous multilayer, and is only 0.98 kOe with the magnetic field in the plane of the film.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358141
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  • 2
    Electronic Resource
    Electronic Resource
    Correlation of x-ray diffraction and Mössbauer effect measurements with magnetic properties of heat-treated Cu80Co15Fe5 ribbons : 38th Annual Conference on Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 6924-6926 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: X-ray diffraction (XRD) and Mössbauer Effect (ME) measurements were performed on heat-treated Cu80Co15Fe5 melt-spun ribbons in an attempt to understand the trends in magnetic properties with heat treatment. ME measurements indicate that the majority of Fe atoms (86%) occupy sites in ferromagnetic FCC CoFe clusters after the initial quench. A heat treatment at 900 °C acts to complete the chemical separation of Fe from the Cu matrix. The presence of Co in the Cu matrix, even after high temperature anneals, provides a paramagnetic component that prohibits saturation even at high fields.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356782
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  • 3
    Electronic Resource
    Electronic Resource
    An improved fabrication technique for porous silicon (1993)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 64 (1993), S. 507-509 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An improved technique for fabrication of porous silicon is described. Silicon wafers of any size and shape can be anodized with this very versatile apparatus. Also, this technique is shown to be safer due to reduced HF acid handling. Overall, this equipment allows more efficient fabrication of uniform and good quality porous silicon safely on silicon wafers of variable sizes and shapes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144223
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  • 4
    Electronic Resource
    Electronic Resource
    The effect of heat treatment on redistribution of fast diffusing impurities in polycrystalline silicon (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 942-944 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of heat treatment on minority carrier surface recombination velocity in polycrystalline silicon samples has been examined in the temperature range (600–900 °C) using the electron-beam induced-current mode of a scanning electron microscope. Minority carrier trap center density, calculated from minority carrier surface recombination velocity data, varying from 8.9×1011 to 6.37×1013 cm−2 have been measured. A finite variation in the minority carrier trap center density indicates that metallic impurities diffuse to the surface from the bulk of the sample. The activation energy of impurity atom diffusion is found to be 1.1±0.1 eV.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.341900
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  • 5
    Electronic Resource
    Electronic Resource
    High-field torque magnetometry measurements on Y1.8Er0.2Fe14B (abstract) (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 3778-3778 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Y1.8Er0.2Fe14B is an interesting system in that the tendency of the Er ions to order in the basal plane is almost exactly canceled at low temperatures by the uniaxial anisotropy of the iron sublattice.1 We have performed torque magnetometry measurements in all three principal planes of a single crystal of this material at temperatures from 4 to 300 K in magnetic fields up to 60 kG, which is adequate to produce near saturation even in directions away from the principal axes, thus allowing us to determine the magnetocrystalline anisotropy free energy as a function of orientation and temperature. The free energy data were compared with calculations using the full set of crystal field parameters allowed by symmetry.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.338640
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  • 6
    Electronic Resource
    Electronic Resource
    Determination of minority-carrier diffusion length in a p-silicon wafer by photocurrent generation method (1986)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 60 (1986), S. 3550-3552 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A nondestructive method to determine the diffusion length of minority carriers in a p-silicon wafer is outlined. This novel method is based on creating an accumulation layer on one side and an inversion layer on the other side of the wafer by depositing thin semitransparent layers of high (e.g., palladium) and low (e.g., aluminum) workfunction metals, respectively. The wafer acquires a structure akin to p+-p-n+ and is capable of generating a photocurrent when illuminated. The photocurrent Isc (where sc represents short circuit) as a function of the intensity Pin of a monochromatic radiation incident on the accumulation layer (p+) side of the wafer is measured. The diffusion length L is determined from the slope of the Jsc vs Pin curve. The values of L so determined were compared with that determined from the measurement of spectral response by illuminating the wafer from the inversion layer (n+) side and were found to be in excellent agreement.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.337610
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  • 7
    Electronic Resource
    Electronic Resource
    Effect of WO3 doping on the properties of YBa2Cu3O7−x superconductor (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 371-375 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Tungsten-doped YBa2Cu3O7−x superconducting samples are characterized with the help of resistivity, crystal structural, microstructural, density d, and critical current density Jc studies for doping concentrations varying from 0.00 to 0.14 mol % of WO3. It has been found that doping of WO3 has hardly any influence of Tc, whereas it seems that d and Jc are affected. d and Jc of the samples increase in the range 0〈WO3≤0.04, but above this range, both start decreasing. The maximum Jc obtained at 77 K and zero magnetic field in YBa2Cu3O7−x doped with 0.04 mol % of WO3 is 450 A/cm2. The lower concentrations (〈0.04 mol %) seem to improve the density, whereas higher concentrations lead to porous structure and also induce the formation of BaCuO2 and Y2Ba1Cu1O5 nonsuperconducting phase as revealed by scanning electron microscopy, energy dispersive spectral, and x-ray diffraction analyses. The x-ray diffraction analysis also showed no appreciable change in the lattice parameters with WO3 doping. It appears that the WO3 doping changes the microstructure of YBa2Cu3O7−x to influence its Jc.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345264
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  • 8
    Electronic Resource
    Electronic Resource
    Phase-separated Fe and Co particles in a BN matrix (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 3320-3322 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using co-sputtering, 10–300 A(ring) particles of Fe and Co have been prepared in an insulating BN matrix. The Fe particles have the α-Fe structure. The saturation magnetic moment of the iron particles per at. % Fe was found to be approximately independent of the Fe concentration and equal to the value of α-Fe. The system undergoes a metal–nonmetal transition at approximately 40 vol % Fe. For concentrations of Fe particles above this threshold the temperature dependence of the resistivity is metallic and the room-temperature coercivity is large (50–100 Oe). For the Co particles, the room-temperature coercivity is about twice as large as Fe above the metal–nonmetal threshold. Below the metal–nonmetal threshold the particles behave as superparamagnets and the coercivity is approximately zero.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.338977
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  • 9
    Electronic Resource
    Electronic Resource
    Mössbauer study of spin reorientation in Y1.8Er0.2Fe14B (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 3568-3570 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Fe57 Mössbauer spectra were taken from 300 K down to 4.2 K for two single-crystal samples of Y1.8Er0.2Fe14B, one cut with its [001] axis normal to the surface, the other with its diagonal of [100], [010], and [001] axes normal to the surface. The former sample has shown that the angle between the Fe spin and the [001] increases continuously below ∼90 K. This qualitatively agrees with the spin reorientation (i.e., the easy axis of magnetization rotates away from the [001] toward [100] on cooling below ∼90 K) which have already been observed by torque magnetometry. The latter sample has shown that the Fe spin actually rotates continuously; abrupt change of Fe spin direction, which have been already suggested to occur in Er2Fe14B, does not occur in Y1.8Er0.2Fe14B. The samples were so thick that the intensity of strong absorption lines were saturated. We have derived a formula with which the saturation effect can be corrected in order to determine the angle of the Fe spin direction correctly.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.338728
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  • 10
    Electronic Resource
    Electronic Resource
    Direct deposition of highly coercive gamma iron oxide thin films for magnetic recording (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 7019-7021 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Direct preparation of high coercivity gamma iron oxide (γ-Fe2O3) thin films by chemical vapor pyrolysis techniques have been described. Films deposited at temperatures above 500 °C have the γ- and those deposited below 500 °C have the α-Fe2O3 phase. Gas phase reactions leading to oxygen deficiency in the vicinity of substrate and consequently controlled in situ oxidation of Fe3O4 appear responsible for direct growth of the γ-Fe2O3 film. Magnetic properties of these films are optimized by adding cobalt. High coercivity values of 3 kOe for directly deposited γ-Fe2O3 films containing 6 at. % of cobalt are obtained along with reasonable values of remanence ≈2.8 kG and squareness ratio of 0.83. These values are considerably superior for magnetic recording in comparison to those for γ-Fe2O3 films obtained by reduction and reoxidation of α-Fe2O3 films.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355062
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