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  • 1
    Electronic Resource
    Electronic Resource
    Scanning tunneling microscopy on rough surfaces-quantitative image analysis (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 523-525 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this communication, the application of scanning tunneling microscopy (STM) for a quantitative evaluation of roughnesses and mean island sizes of polycrystalline thin films is discussed. Provided strong conditions concerning the resolution are satisfied, the results are in good agreement with standard techniques as, for example, transmission electron microscopy. Owing to its high resolution, STM can supply a better characterization of surfaces than established methods, especially concerning the roughness. Microscopic interpretations of surface dependent physical properties thus can be considerably improved by a quantitative analysis of STM images.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350267
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  • 2
    Electronic Resource
    Electronic Resource
    Evolution of the dielectric breakdown in Co/Al2O3/Co junctions by annealing (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 586-589 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The temperature and dielectric stability of magnetic tunnel junctions are important requirements for magnetic memory devices and their integration in the semiconductor process technology. We have investigated the changes of the tunneling magnetoresistance (TMR), the barrier properties (height, thickness, and asymmetry) and the dielectric stability upon isochronal annealing up to 410 °C in Co/Al2O3/Co junctions with an artificial antiferromagnet as a pinning layer. Besides a small decrease of the TMR signal after annealing up to 230 °C, a strong decrease between 300 and 350 °C is found. According to Auger and transmission electron microscopy investigations, this decrease is mainly due to interdiffusion of the metallic layers. The dielectric breakdown is characterized by voltage ramp experiments. The size-averaged breakdown voltage improves from 1.35 V for the as prepared junctions to 1.55 V by annealing at 300 °C. At higher temperatures the breakdown voltage decreases strongly to 0.8 V (at 380 °C). Simultaneously, the typical breakdown process changes from few sudden current jumps to a large number of small steps. The breakdown properties are discussed within a statistical model and related to structural changes of the barrier. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1329352
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  • 3
    Electronic Resource
    Electronic Resource
    Temperature stability of Co/Al2O3/Co junctions (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 5191-5193 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The temperature stability of magnetic tunnel junctions is an important requirement for the fabrication of magnetic memory devices and the integration in the semiconductor process technology. We have investigated the temperature evolution of the tunneling magnetoresistance (TMR) and the structural properties by isochronal annealing experiments up to 750 K. The magnetically hard electrode of the junction consists of an artificial antiferromagnet Co/Cu/Co, the soft electrode of a Co/Fe bilayer. The tunnel barriers are formed by plasma oxidized Al. The tunnel junctions have TMR signals up to 22% at room temperature. Besides a small increase of the TMR signal after annealing up to 480 K, a first decrease at 530 K and a breakdown beyond 600 K are found. This behavior can be attributed to structural changes of the junctions. Auger depth profiles show an unaltered Al2O3 barrier up to 600 K, but the beginning of interdiffusion processes within the magnetic electrodes already at 540 K and above. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373291
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  • 4
    Electronic Resource
    Electronic Resource
    3D-simulations of magnetic structures in af-coupled multilayers with pinholes (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 6597-6599 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: For antiferromagnetically (af) coupled Py (Ni81Fe19|Cu)-multilayers lattice calculations have been used already for the investigation of pinholes in GMR elements. The very thin spacer layer (〈10 Å) is sensitive against pinholes as a link between the magnetic layers. Additional coupling through the pinhole modifies drastically the af-coupling between the magnetic layers and leads to strong changes in the M(H) and ΔR/R(H) curves. Improved lattice calculations with large grids offer the opportunity, to study effects of geometry in layers structured laterally. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372782
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  • 5
    Electronic Resource
    Electronic Resource
    Interplay of antiferromagnetic coupling in copper/permalloy combination multilayers (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 4849-4851 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The evolution of the giant magnetoresistance (GMR) effect in sputtered combination multilayers (CMLs) of type Py1.8nm//{(Cu1.8nm/Py1.6nm)N/(Cu0.9nm/Py1.6nm)N}y with Py (permalloy=Ni81Fe19) has been investigated at room temperature. It is shown that the GMR characteristic of these CMLs can be phenomenologically predicted, if the physical properties are known, i.e., the GMR effect amplitude, double layer conductance, and bilinear and biquadratic antiferromagnetic exchange coupling constants of the two underlying {Cu/Py}N base systems at the first (Cu0.9nm) and second (Cu1.8nm) antiferromagnetic coupling maximum (AFCM). The GMR characteristic of the simplest CML with N=1 is, e.g., determined by averaging the bilinear and biquadratic exchange coupling constants of the two base systems. The GMR characteristics of CML with N≥2 are a superposition of that of the underlying {Cu/Py}N base systems weighted by the fraction of the corresponding double layer conductance. Furthermore, it is demonstrated that the CMLs are interesting from an application point of view since they combine the temperature stability of the underlying {Cu/Py}N base system at the second AFCM with a larger GMR effect amplitude. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373179
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  • 6
    Electronic Resource
    Electronic Resource
    Adjustment of temperature coefficient of resistance in NiCr/CuNi(Mn)/NiCr films (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 8516-8520 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The thin-film system Ni0.37Cr0.63/Cu0.57Ni0.42Mn0.01/Ni0.37Cr0. 63 with a typical thickness of 1 μm is used for low-ohmic precision resistors. The necessary adjustment of the temperature coefficient of resistance (TCR) by annealing has been studied by investigating the irreversible changes of the resistance during various annealing steps of NiCr/CuNi(Mn)/NiCr multilayers in comparison with single layers of CuNi(Mn) and NiCr. Auger depth profiles showed that the interdiffusion of CuNi(Mn) and NiCr results in an impoverishment of Ni in CuNi(Mn), explaining the TCR shift by comparison with data of Cu1−xNix bulk material. The decrease of the resistivity and the reduction of the width of the copper-nickel conductive layer by formation of a Ni0.6Cr0.2Cu0.2 interdiffusion zone phase (in accordance with the Cu-Ni-Cr phase diagram) cause a significant curvature of the resistance-temperature curve. As main result, it is shown that the NiCr base and cover layers and their interdiffusion with CuNi(Mn) play the decisive role in adjusting the TCR. It was checked that oxidation and topography effects have no remarkable influences. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362531
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  • 7
    Electronic Resource
    Electronic Resource
    Scanning tunneling microscopy on rough surfaces: Deconvolution of constant current images (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 57 (1990), S. 867-869 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This letter critically discusses the topographical information obtained by scanning tunneling microscopy (STM) on surfaces with a mesoscopic roughness, i.e., in the range of some nm's. In a foregoing publication [J. Appl. Phys. 67, 1156 (1990)], we already treated the evaluation of constant current images based on the knowledge of the real surface and the shape of the tunneling tip ("tip shape limited resolution''). Now we deal with the invers problem: the reconstruction of the real surface topography based on the corresponding STM image and the tip shape, using a simple, straightforward formalism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.103390
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  • 8
    Electronic Resource
    Electronic Resource
    Optimization processes of giant magnetoresistance characteristic for mixed magnetic multilayers (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 993-998 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Up to now, giant magnetoresistance (GMR) multilayers usually consist of only one type of double layer (e.g., permalloy/copper). In this work, we report on results obtained on mixed systems, i.e., multilayers containing simultaneously the first and second maximum of the antiferromagnetic coupling. Both a phenomenological numerical approach as well as experimental results demonstrate, that such systems can be used for tailoring new shapes of GMR curves. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373767
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  • 9
    Electronic Resource
    Electronic Resource
    Evolution of barrier asymmetry in magnetic tunnel junctions (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 1113-1115 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetic tunnel junctions usually consist of different layer stacks at the two sides of the tunneling barrier. The exposure of these junctions to high temperatures thus can induce large asymmetries in the electronic potential with respect to the barrier. Using the example of Co/Cu/Co/Al2O3/Co tunnel junctions, we show that the measured current/voltage characteristics develop a large asymmetry upon annealing at a temperature larger than 230 °C. This is accompanied by a Cu enrichment at one side of the barrier and cannot be explained by simply using the work function differences between the electrode materials. Thus, a Cu–Al2O3 intermixing zone at the barrier interface must be taken into account, which leads to an asymmetric step-like barrier shape. The interpretation is supported by numerical evaluation of model barriers which reproduce the experimental asymmetries if an intermixing zone of only 0.2 nm thickness is assumed. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1350601
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  • 10
    Electronic Resource
    Electronic Resource
    Switching stability of magnetic tunnel junctions with an artificial antiferromagnet (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 3456-3458 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Avoiding fatigue in the switching of magnetic tunnel junctions is crucial for their long-term use in nonvolatile magnetic memories. We compare the switching stability of two types of junctions with different soft layers: Fe or Ni81Fe19, both with Co dusting at the barrier interface. The magnetically hard electrode is a Co/Cu/Co artificial antiferromagnet. While the tunneling magnetoresistance (TMR) remains unchanged after 104 cycles in a 4 kA/m rotating field, it decreases by more than 45% due to uniaxial switching. Fringing fields of domain walls in the soft layer and an intrinsic instability of Co/Cu/Co are identified as the main reasons. Magnetization reversal by two perpendicular switching pulses avoids this magnetic degradation and maintains a full TMR signal. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1327272
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