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  • 1
    Electronic Resource
    Electronic Resource
    Interface chemistry and structure of multiply oxidized barrier spin-tunnel junctions (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 5200-5202 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Nb/Fe/Al2O3/CoFe/Nb spin-tunnel junctions fabricated using a multiple oxidation technique have been characterized using high spatial resolution electron microscopy techniques. Junction magnetoresistance values up to 6.2% at room temperature and 9.2% at 77 K were obtained for junctions fabricated using this technique. Energy dispersive x-ray spectroscopy and electron energy loss spectroscopy were used to study the chemistry and interface structure of the barrier layer; elemental mapping showed the degree of chemical homogeneity across the layers and high spatial resolution electron energy loss spectroscopy revealed changes in the oxidation state and d-shell occupancies of Fe and Co across the layers, which need to be considered when modelling the spin-tunneling effect. Pinholes across the barrier were also observed by high resolution electron microscopy. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373294
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  • 2
    Electronic Resource
    Electronic Resource
    Magnetization reversal processes in exchange-biased systems (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 6412-6414 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetization reversal mechanism in sputtered bilayer films of NiFe coupled to a range of antiferromagnets has been studied using Lorentz microscopy and magnetic measurements. The reversal mechanism on the forward and recoil loops appears different and the results have been interpreted in terms of a recently published seven-point model. Reversal is controlled by the magnetic domain structure in the antiferromagnet. Time-dependent studies show that the reversal field for the NiFe layer decreases for both the forward and recoil loops, as the time for which the film is held above the saturation field of the NiFe layer increases. This can be explained by viscous rotation of the magnetization in thermally activated domains in the antiferromagnetic layer. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372722
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  • 3
    Electronic Resource
    Electronic Resource
    Effect of stray-field coupling on active spin-valve elements analyzed by Lorentz transmission electron microscopy (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 4120-4126 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In situ experiments using Lorentz transmission electron microscopy have been performed on 10 μm×30 μm active spin-valve elements through which a current is applied during observation of the magnetization reversal of the sense layer. It is shown that the reversal mechanism and the change in resistance are very different depending on the relative orientations of the easy axis versus the applied field. The results show clearly that the contributions of the magnetostatic fields, due to either ferromagnetic coupling or stray-field coupling, are higher than that of the field induced by the sensing current. A model is proposed to predict the offset of the giant magnetoresistance curves with respect to zero field. This model has been found to be in good agreement with the experimental results. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370320
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  • 4
    Electronic Resource
    Electronic Resource
    Effect of ferromagnetic layer structure on the magnetization process in NiFe/Co/Al–O/NiFe and Co/NiFe/Al–O/NiFe junctions (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 5753-5755 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of ferromagnetic layer structure on the magnetization reversal processes in (NiFe/Co)/Al–O/NiFe (S1) and (Co/NiFe)/Al–O/NiFe (S2) films was investigated. The films were fabricated by sputter deposition, and the Al–O layer was prepared by oxidizing an Al layer in air. Two distinct magnetization processes were observed by transmission Lorentz microscopy (TLM) with increasing in situ applied field. Reversal of the NiFe/Co bilayer in S1 occurs via moment rotation, while reversal of the Co/NiFe bilayer in S2 occurs by domain wall motion, in both cases at higher field than the top NiFe layer. The difference can be ascribed to the difference in the deposition order of the ferromagnetic bilayers (FMBs). High resolution electron microscopy shows that the grains in the top NiFe layer are randomly oriented in both films. In S1, the NiFe grains in the FMB are randomly oriented, with columnar grains present in the Co. In S2, a columnar grain structure of NiFe in the FMB is induced by the Co underlayer. The rough FMB/Al–O interface in S2 leads to weak biquadratic interlayer coupling, which will slightly reduce the field range of the antiparallel magnetization configuration. Hysteresis loops of S1 and S2 show two stage magnetization reversals in each sample, which are consistent with TLM results. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370115
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  • 5
    Electronic Resource
    Electronic Resource
    Structure and chemistry of manganite based tunnel junctions (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 6757-6759 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Half-metallic manganite (La0.7Ca0.3MnO3) based spin tunnel junctions with two barrier layers (NdGaO3 and La0.45Ca0.55MnO3) have been investigated structurally as well as chemically using high spatial resolution electron microscopy techniques. Both junctions were grown on a NdGaO3 substrate, which has better lattice match compared to a more traditional substrate such as strontium titanate (SrTiO3). Devices with a NdGaO3 barrier showed tunnel magnetoresistance (TMR) values up to 85% at 77 K, whereas the devices with a La0.45Ca0.55MnO3 barrier layer showed only 18% TMR at 77 K. The electron microscopy data show much clearer, sharper interfaces, structurally as well as chemically, for NdGaO3 than for the La0.45Ca0.55MnO3 barrier layer. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1357834
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  • 6
    Electronic Resource
    Electronic Resource
    Study of magnetic thin films deposited by closed-field unbalanced magnetron sputtering (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 5747-5749 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Closed-field unbalanced magnetron sputtering, developed by TEER Coatings Ltd., uses a novel plasma confinement system, which allows controllable high-rate deposition from a wide range of target materials. We report the first use of this technique using ferromagnetic target materials to grow films of nanometer thickness. A study was carried out on a series of Py/Cu/Py and Py/Au/Py magnetic multilayer films, with and without underlayers of Ti or Ta. High-resolution electron microscopy showed that 5 nm of Ti or 15 nm of Ta did not change the structure of the trilayers. The use of Au as a spacer layer induced a texture in the upper Py layer, which decreased its saturation field by half. In situ experiments to observe the effects of an applied field on the domain structure of the films were carried out using Lorentz transmission electron microscopy. Variations in the switching field of the Py layers and of the coupling strength between the Py layers were observed when the thicknesses of the three layers were varied. Double domain wall structures with different wall intensities were observed in some cases. The roughness of the interfaces were increased by ion bombardment; this increased the saturation field of the Py layers. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370113
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  • 7
    Electronic Resource
    Electronic Resource
    Improved Foucault imaging of magnetic domains with a modified 400 kV transmission electron microscope (1993)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 64 (1993), S. 1038-1043 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Modifications have been made to a 400 kV side-entry transmission electron microscope fitted with a low-field objective pole piece, in order to position apertures close to the back focal plane of the objective lens, as there is no direct access to the required position in the column. The modifications have facilitated developments in the imaging of magnetic domain structure in magnetic materials using the Foucault technique, for which the correct positioning of the objective aperture is crucial. All usual transmission electron microscopy facilities are retained, allowing a full range of specimen holders and imaging modes to be used along with TV recording and electron energy loss spectroscopy. Some initial results are presented from Fe/Cr and Co/Pt multilayer films, for which the Lorentz deflection angle is very small, and for which the Fresnel imaging mode is of limited use as the grain structure contrast masks the magnetic contrast. Initial results are also presented from NdFeB permanent magnet material for which the use of a high electron accelerating voltage is necessary.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144174
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  • 8
    Electronic Resource
    Electronic Resource
    Studies of Fe/Cr multilayer and trilayer films : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 6292-6294 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Series of sputter-deposited Fe3 nm/Crx multilayer and Fe/Cr/Fe trilayer films have been analyzed. The small magnetoresistance exhibited by the multilayer films is attributed to very rough interfaces and poor Cr layer quality. The hysteresis loop data show the interlayer exchange coupling to be predominantly antiferromagnetic. In situ magnetizing of the trilayer films in a Lorentz TEM showed that for a 1.2 nm thick Cr layer the moments of the Fe layers lie approximately parallel at remanence rotating to antiparallel only when the field is increased. The magnetic moments in an Fe12 /Cr0.6 nm/Fe12 nm trilayer film were found to be parallel aligned under an applied field whereas the hysteresis loop for the multilayer films with the same Cr thickness suggest the existence of antiferromagnetic interlayer exchange coupling. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362040
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  • 9
    Electronic Resource
    Electronic Resource
    Structure and magnetic properties of Co/Cu multilayer films (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 2387-2394 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The structure, magnetic properties and magnetoresistance of Co/Cu multilayer films grown by sputtering on Si (100) wafers, with Co layer thicknesses between 1.9 nm and 2.0 nm and Cu layer thicknesses between 0.5 nm and 1.3 nm, have been studied. X-ray diffraction, transmission electron microscopy, and optical diffractogram analysis show layered structures and a columnar face-centred-cubic (111) crystallographic texture extending through several layers in the films. The magnetic domain structure was studied by Lorentz microscopy, and the domain structure and image contrast were found to depend strongly on the Cu layer thickness and magnetoresistance. Hysteresis curves explain the trends of magnetic domain contrast and magnetic coupling in the films. Annealed samples show a more regular domain structure, and lower saturating field and magnetoresistance than as-sputtered samples.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357586
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  • 10
    Electronic Resource
    Electronic Resource
    A microstructural study of annealed Ti/Co/Cu/Co/MnFe/Ti spin-valve films (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 118-120 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Spin-valve properties are adversely affected by heat treatments and in order to study this effect, microstructural analyses of Ti/Co/Cu/Co/MnFe/Ti spin-valve films annealed at 225 and at 290 °C have been performed. Whereas the lower temperature tends to optimize the giant magnetoresistance (GMR) ratio, the higher temperature induces a significant decrease in the GMR ratio (from 7.5% to 5.2%). High resolution electron microscopy studies have explained this result as being due to the formation of a TiCo alloy at the Ti/Co interface and to a decrease in the thickness of the sense layer. No significant modification of either the Co/Cu or the Cu/Co interfaces has been observed. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.120662
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