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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 431-439 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: To determine the molecular orientation of rubbed and unrubbed poly[4,4′-oxydiphenylene- pyromellitimide] (PMDA-ODA) films, we have measured the infrared (IR) absorption spectra of PMDA-ODA films on Si substrates as a function of the incident angle. The molecular orientation was determined by fitting the incident angle dependence and the IR dichroic ratio with the theoretical curves. The IR absorption was calculated by a transfer matrix method to take account of the multiple reflection and refraction at the interfaces. The vibrational response of the polyimide film in the IR region was represented by a Lorentz oscillator model. We found that the molecules in a spin-coated polyimide film are oriented parallel to the substrate surface with a standard deviation of 6.5°. For a rubbed film, the polymer chains are oriented along the rubbing direction and are tilted up on average by 8.5° from the surface plane. We observed a blueshift of the C=O asymmetric stretching band at oblique incidence. The blueshift is explained by anomalous dispersion of the dielectric constant of the polyimide film, and is reproduced by our calculation. © 1996 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 79 (1996), S. 4193-4196 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We find two different surface structures, (1×2) and (1×1), for H2S-treated InP(001). They depend upon exposure of H2S at about 350 °C. The coverage of sulfur is estimated to be about a half monolayer and one full monolayer for the (1×2) and (1×1) structures, respectively. The (1×1) structure is reconstructed to the (1×2) structure upon annealing at about 550 °C. It is suggested that sulfur is bonded to only In atoms and substitutes some of the phosphorus atoms below the first layer. Inverse photoemission spectra show strong reduction in intensity of 1.2 eV peak above the Fermi level for a clean InP(001)-(4×2) surface upon adsorption of H2S. This reduction implies a decrease in unoccupied surface states due to dangling bonds of indium dimers on the clean surface. The result of adsorption of oxygen on the (1×2) and (1×1) surfaces indicates significant passivation to oxidation of the surfaces. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A Co/Pt multilayer is one of the most attractive candidates for next-generation high-density magneto-optical recording media. With a decreasing Co layer thickness, the direction of the easy axis of magnetization changes from in-plane to out-of-plane. We have measured core-level MCD of Co/Pt multilayers. Six Co/Pt multilayer samples were prepared which had Co layer thicknesses from 3 to 14 A(ring). The MCD experiments were made using circularly polarized undulator radiation.The spectra were taken separately for the energy regions around the Co M2,3 (and Pt O3) and Pt N6,7 (and Pt O2) edges. The dichroic signals in reflectivity were recorded for two opposite directions of an external magnetic field of 2 T. We have also measured the reflectivity spectra down to 4 eV and have made Kramers–Kronig analyses to obtain the dielectric tensor. The dielectric tensor element which represents absorption MCD shows a dramatic change at the Co M2,3 edges. The MCD spectra of thinner Co-layer samples are more asymmetric than those of thicker ones. This shows that the orbital magnetic moment of Co is enhanced as the Co layer thickness decreases. The MCD spectra become sharper and narrower with a decreasing Co layer thickness. This feature strongly reflects a band narrowing of the Co 3d state at or around the Co/Pt interfaces. The MCD spectra at the Pt N6,7 edges show little dependence on the Co layer thickness. This can be explained by assuming that Pt atoms only at the interfaces are responsible for the MCD signals, since the surface density of Pt atoms is equal for all the samples. Combining the result at the Co M2,3 edges with that at the Pt N6,7 edges leads to the conclusion that perpendicular magnetic anisotropy mainly depends on the electronic structure of Co at Co/Pt interfaces and that Pt atoms at the interfaces play a partial role in magnetic anisotropy. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have fabricated and studied the structure and magnetic properties of high quality single crystalline (Mn,Zn)Fe2O4, NiFe2O4, and CoFe2O4 films. Although (Mn,Zn)Fe2O4 and NiFe2O4 films grown directly on SrTiO3 and MgAl2O4 show mediocre structural and magnetic properties, these same films grown on SrTiO3 and MgAl2O4 buffered with CoCr2O4 or NiMn2O4 exhibit excellent crystallinity and bulk saturation magnetization values, thus indicating the importance of lattice match and structural similarity between the film and the underlying layer. X ray, Rutherford backscattering spectroscopy, atomic force microscopy, and transmission electron microscopy analysis provide a consistent picture of the structural properties of these ferrite films. © 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 81 (1997), S. 4989-4989 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Single-crystal bilayers of (magnetically soft) (Mn,Zn)Fe2O4 and (magnetically hard) CoFe2O4 can exhibit nearly ideal exchange anisotropy. This is directly related to the extremely high structural quality that can be achieved by epitaxial growth on appropriate substrates. For example, we use (110)-oriented MgAl2O4 substrates with 100 nm CoCr2O4 buffer layers. The paramagnetic buffer layer provides a close lattice match for the ferrites, and is annealed at about 1000 °C to provide excellent crystallinity. Subsequent growth of the ferrite bilayer is executed at 400 °C, which is high enough to permit growth of highly crystalline epitaxial films, yet low enough to avoid substantial intermixing at the interfaces. Measurements at elevated temperatures (290 K〈T〈1000 K) permit characterization of the exchange anisotropy in regimes of low and moderate crystal anisotropy in the soft layer, as well as directly revealing the blocking temperature and the portion of the overall magnetization contributed by each layer. The results provide additional evidence that the exchange coupling energy across the interface is comparable to that within each layer, and in that sense is nearly ideal. The detailed shapes of the M–H loops are found to be in semiquantitative agreement with micromagnetic theory. ©1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Amorphous/crystalline bilayers of NiFe2O4 exhibit interlayer magnetic exchange coupling, which results from an interaction between a spin-glass material and a ferrimagnetic material. The observed effect is reminiscent of the well-known exchange coupling effect between an antiferromagnet and a ferromagnet, which is widely used in applications where field biasing of thin magnetic films is desirable. © 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 87 (2000), S. 5618-5620 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetization process in microfabricated NiFe wires was observed using a Kerr microscope. Magnetic wires were made from a 20-nm-thick NiFe film by using lift-off techniques. Their width W and length L were designed as W=0.5, 1.0 and 2.0 μm and L=50 μm, respectively. One end of the wire was connected to a square shaped head with a side of 2W, which is designed to act as a domain wall source. In each wire, necks with different width of 0.2W, 0.6W, and 0.8W were introduced as artificial pinning sites of a domain wall. By using an oil-immersion lens (NA=1.3) and a Hg lamp, magnetization reversals in very narrow wires, as narrow as 0.5 μm, were clearly observed. It is confirmed that domain wall penetration, pinning, depinning, and also the direction of wall motion are controllable using square shaped head and necks with optimized width. © 2000 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 85 (1999), S. 4797-4799 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have performed magnetization and magnetoresistance measurements on (110)La0.7Sr0.3MnO3 thin films in order to understand the role of in-plane uniaxial magnetic anisotropy in the magnetoresistance. Transport measurements with current flowing along the magnetically easy [001] and magnetically hard [11¯0] directions exhibit a linear dependence of magnetoresistance on field at high fields due to bulk colossal magnetoresistance. The low field behavior depends not only on the angle of the magnetization with the current but also the direction of the current in the crystal. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 6746-6748 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Our studies of compressively strained La0.7Sr0.3MnO7 (LSMO) thin films reveal the importance of domain structure and strain effects in the magnetization reversal and magnetotransport. Normal and grazing incidence x-ray diffraction indicate that the compressive strain on these LSMO thin films on (100) LaAlO3 is not completely relaxed up to thicknesses on the order of 1000 Å. The effect of the compressive strain is evident in the shape of the magnetization loops and the magnetotransport measurements at various temperatures. Although the domain wall contribution to the magnetoresistance is significantly larger than that predicted from a simple double exchange picture, the contribution is a small fraction of the measured magnetoresistance. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 404-409 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the switching behavior of single-domain cobalt nanostructures using a combination of magnetometry and magnetic force microscopy. The elongated nanostructures are 80×140 nm wide, and range in thickness from 14 to 30 nm. Structures thinner than 20 nm form a single-domain binary system featuring two preferred orientations of the magnetization. An additional double-domain configuration becomes increasingly favorable as the thickness approaches 30 nm. The onset of this double-domain state agrees with previously reported numerical calculations. We also present a quantitative study of interparticle coupling in tightly packed arrays. The local dipolar field increases the squareness of the hysteresis loop as the interparticle separation decreases below 400 nm. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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