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  • 1
    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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  • 2
    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.
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  • 3
    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.
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  • 4
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated the properties of NiFe2O4 thin films prepared by laser ablation of a stoichiometric NiFe2O4 target. Textured polycrystalline films were obtained on a-SiO2 as well as on various substrates with Au, Ag, Pt, and MgF2 buffer layers. Epitaxially oriented films were obtained on MgO, (11¯02)-oriented Al2O3, (112¯0)-oriented Al2O3, Y-stabilized ZrO2 (YSZ), and SrTiO3, although the crystalline quality of the films varied. Contamination by diffusion from the substrate and strains induced by both lattice constant mismatch and differential thermal expansion degraded the magnetic properties of the films, and in some cases decreased the electrical resistivity as well. By choosing the right substrate (YSZ), temperature (600 °C), and PO2 (0.01 mT), we are able to prepare epitaxial films with bulk saturation magnetization (Ms=270 G) and fairly low anisotropy (K∼105 erg/cm3) as inferred by torque magnetometry. These films and bilayers are expected to be useful in a variety of fundamental investigations as well as having the potential for technological applications.
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 2847-2851 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The microstructure of oxidized amorphous Tb-Fe alloy thin films prepared by magnetron cosputtering has been studied as a function of alloy composition and the substrate temperature at which the films were grown. Transmission electron microscopy and Auger electron spectroscopy with ion-sputter depth profiling were used to characterize the films. The composition of the alloy has no dramatic effect on the oxidation rate; it does, however, effect the microstructure of the α-Fe2O3 layer that forms on the alloy. Oxidized alloys originally containing more than 27 at. % Tb show an extremely fine-grained structure, with grain sizes on the order of 30 A(ring). Alloys containing less Tb developed large (1–2 μm) [001]-oriented single-crystal α-Fe2O3 grains amongst the fine-grained α-Fe2O3. For alloys with less then 18 at. % Tb, only the large grains remain. Samples grown at deposition temperatures ranging from 85 K to 400 °C show a similar structure after oxidation.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 3543-3545 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We describe a new class of low-carrier-density magnetic materials based on lanthanide-substituted scandium and yttrium pnictides. In general, these III-V compounds have energy gaps in the vicinty of 1 eV, and like most of the lanthanide pnictides, form in the B1 (rocksalt) structure. Substitution of rare earths for Y or Sc to form solid solutions is readily achieved. For example, we have produced GdxY1−xN by reactive magnetron cosputtering, and obtained epitaxial growth on sapphire substrates resulting in high-quality single-crystal thin films. These films exhibit moderately low carrier densities and high mobilities, and have interesting magnetic properties at low temperatures. In this paper we present a preliminary look at some of the properties of these materials.
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 1103-1107 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recent reports of huge magneto-optical Kerr rotations in certain crystalline metallic uranium compounds prompted a study of the magnetic and magneto-optical effects of uranium additions to a rare-earth transition metal amorphous alloy. Using variable composition samples, the polar Kerr effect at a small spot (e.g., 0.5 mm diam) was measured as field, temperature, and composition were varied. Points on the Curie line and the edges of the compensation region were determined from these observations. The compositions studied included (TbxFe1−x)1−yUy with 0.125≤x≤0.550 and y=0.0, 0.04, 0.07, 0.16. The addition of uranium to TbxFe1−x depresses the TC of Tb-rich material much more strongly than that of Tb-poor material. The compensation region does not shift at all with increasing y. It appears that uranium does not contribute to the magnetization of these amorphous alloys, nor does it significantly affect the magneto-optical effects.
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 850-862 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ta2O5 is a candidate for use in metal–oxide–metal (MOM) capacitors in several areas of silicon device technology. Understanding and controlling leakage current is critical for successful implementation of this material. We have studied thermal and photoconductive charge transport processes in Ta2O5 MOM capacitors fabricated by anodization, reactive sputtering, and chemical vapor deposition. We find that the results from each of these three methods are similar if one compares films that have the same thickness and electrodes. Two types of leakage current are identified: (a) a transient current that charges the bulk states of the films and (b) a steady state activated process involving electron transport via a defect band. The transient process involves either tunneling conductivity into states near the Fermi energy or ion motion. The steady state process, seen most commonly in films 〈300 Å thick, is dominated by a large number of defects, ∼1019–1020 cm−3, located near the metal–oxide interfaces. The interior of thick Ta2O5 films has a substantially reduced number of defects. Modest heating (300–400 °C) of Ta2O5 in contact with a reactive metal electrode such as Al, Ti, or Ta results in interfacial reactions and the diffusion of defects across the thickness of the film. These experiments show that successful integration of Ta2O5 into semiconductor processing requires a better understanding of the impact of defects on the electrical characteristics and a better control of the metal–Ta2O5 interface. © 2000 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 6304-6306 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A type of surface acoustic wave (SAW) device is introduced in which coupling between the transducer and the acoustic medium is achieved using a magnetostrictive thin film. These magnetically transduced SAW devices have several advantages over conventional piezoelectric SAWs, and may expand the functionality of SAW devices in general. Several possible designs are presented, along with data from two prototypes. Results from these devices are promising, and they indicate that several acoustic modes, both surface and bulk, can be stimulated. © 2000 American Institute of Physics.
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 3136-3143 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: NbN thin films cosputtered with Ta show approximately an order of magnitude enhancement in critical current density over a wide range of applied magnetic fields, while the critical fields and transition temperatures are essentially unchanged by the Ta addition. Both thin-film x-ray diffraction and cross-sectional transmission electron microscopy analyses show a highly textured structure with a second phase (also highly textured) present in these films at the grain boundaries. The Ta acts to refine the grain size of the NbN, increasing the effective pinning strength and hence the critical current density. Comparison of the global pinning force to current models of flux pinning supports individual pin breaking as the limiting mechanism for critical current in NbN films.
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