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1

Digitale Medien

Periodicity and surface flux closure of multipolar 180° Bloch walls (1987)

Hartmann, U.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 62 (1987), S. 621-626

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: The recent calculation of the specific energy associated with Néel singularities in cubic crystals now permits an estimation of the periodicity and self-magnetostatic energy of multipolar 180° Bloch walls. Additionally, it is shown that the slight zigzagging of these walls in the near-surface region of a crystal causes a considerable reduction of the effective free surface charges by an extensive flux closure internal to the crystal

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.339790

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2

Digitale Medien

Fiber interferometer-based variable temperature scanning force microscope (1997)

Euler, R. ; Memmert, U. ; Hartmann, U.

[S.l.] : American Institute of Physics (AIP)

Review of Scientific Instruments 68 (1997), S. 1776-1778

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ISSN: 1089-7623

Quelle: AIP Digital Archive

Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik

Notizen: A scanning force microscope designed for an operation at temperatures between 4.2 and 300 K is presented. The deflection of the microfabricated force sensing cantilever is detected via an optical fiber interferometer. For low temperature imaging the whole instrument is incorporated into a bath cryostat which is suitable for both liquid helium and liquid nitrogen cooling. The instrument is of highly symmetric design in order to avoid large inner misalignment of the interferometer due to thermal expansion/contraction during temperature changes. In addition to this thermally compensated design, the interferometer can be adjusted by piezo actuators in situ in three dimensions. © 1997 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.1147992

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3

Digitale Medien

Combined ultrahigh vacuum scanning tunneling microscope scanning electron microscope system (1996)

Memmert, U. ; Hodel, U. ; Hartmann, U.

[S.l.] : American Institute of Physics (AIP)

Review of Scientific Instruments 67 (1996), S. 2269-2273

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ISSN: 1089-7623

Quelle: AIP Digital Archive

Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik

Notizen: We describe a combined ultrahigh vacuum scanning tunneling microscope (STM)–scanning electron microscope (SEM) system, which allows to position the STM tip with respect to the sample within an area of 5 mm×5 mm under SEM control. While the SEM resolution is sufficient to clearly resolve sub-μm structures on the samples, the STM features atomic resolution on semiconductor surfaces. The combination of SEM and STM allows high-resolution studies on inhomogeneous samples in materials research as well as the use for micro- and nanoelectronic device characterization or device modification. The STM performance was checked by atomically resolved imaging of Si(111) (7×7) surfaces. The STM/SEM combination and its application in device characterization is demonstrated by the investigation of vertically grown resonant tunneling diodes on an AlAs/GaAs basis. Due to its performance the system has a high potential for high-resolution imaging in materials research, for novel device characterization and nanoscale structuring or modification of very small devices. © 1996 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.1147045

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4

Digitale Medien

In situ observation of interactions between Bloch walls and local crystalline defects (1988)

Hartmann, U.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 63 (1988), S. 167-171

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: The influence of local crystalline defects upon the magnetization reversal process of single-crystalline iron whiskers has been investigated by direct observation of the domain configuration and by inductive magnetization measurements. As an essential result, the investigations bring to evidence that only weak interactions are obtained between the dislocations and 180° Bloch walls. On the other hand, a strong pinning efficiency to 90° Bloch walls is observed which is due to the stress field created by the perturbation.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.340484

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5

Digitale Medien

Observation of subdivided 180° Bloch wall configurations on iron whiskers (1986)

Hartmann, U. ; Mende, H. H.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 59 (1986), S. 4123-4128

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Subdivided 180° Bloch walls have been observed on iron whiskers using an improved colloid technique. Under the influence of a magnetic field applied vertical to the surface of a specimen the magnetization reversal of the complex wall is governed by Néel line motion. The field-induced conversion exhibits a characteristic "remanence'' and "coercivity'' of the wall. During a longitudinal magnetization cycle of a whisker the actual wall configuration has a substantial influence on the magnetization curve. The coercivity of the specimen is closely correlated to the initial mobility of the Néel lines. Discontinuities in the Néel line motion are responsible for small Barkhausen jumps, especially in the low-field region. The irregular segmentation of the complex wall in the remanent state appears to be an essential source of the remanent whisker magnetization.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.336670

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6

Digitale Medien

Magnetic force microscopy: Some remarks from the micromagnetic point of view (1988)

Hartmann, U.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 64 (1988), S. 1561-1564

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: The present communication focuses on a critical micromagnetic discussion of the promising analytical possibilities with regard to ferromagnetic fine structures offered by the recent invention of magnetic force microscopy. As a result, some limiting constraints for the analysis of soft and hard ferromagnetic media are derived which have to be taken into account for an interpretation of the experimental results.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.341836

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7

Digitale Medien

Néel-line motion along Bloch walls (1987)

Hartmann, U.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 62 (1987), S. 4918-4920

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: The motion of Néel lines along subdivided 180° Bloch walls has been investigated on iron whisker single crystals by indirect optical observation through the influence on Bitter patterns. The field-induced displacement of the lines is dominated by microscopic Barkhausen jumps, where the lines exhibit a striking flexibility along their longitudinal extent. Phenomena such as line fusion, line nucleation, and interactions with crystal defects have been investigated more closely.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.339001

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8

Digitale Medien

Improved magnetic fine-structure analysis by simultaneous observation of domains and walls (1987)

Hartmann, U.

Woodbury, NY : American Institute of Physics (AIP)

Applied Physics Letters 51 (1987), S. 374-375

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ISSN: 1077-3118

Quelle: AIP Digital Archive

Thema: Physik

Notizen: An optical technique is presented which permits a simultaneous observation of domains and domain boundaries in transparent and opaque magnetic specimens. The Faraday or Kerr contrast combined with Bitter pattern agglomerations yields a maximum information transference for an investigation of magnetic fine structures. Some results obtained for a uniaxial ferrimagnetic film are discussed.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.98446

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9

Digitale Medien

Anisotropic low-field magnetoresistance of polycrystalline manganite sensors (1999)

Xu, Yunhui ; Dworak, V. ; Drechsler, A. ; [weitere]

Woodbury, NY : American Institute of Physics (AIP)

Applied Physics Letters 74 (1999), S. 2513-2515

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ISSN: 1077-3118

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Magnetic-field sensors of bulk La0.67Sr0.33MnO3 and La0.67Ba0.33MnO3 were fabricated. The investigations show that a large low-field magnetoresistance (MR) is exhibited by the polycrystalline samples. MR ratios of the sensors as large as 20% at 77 K and 1.5% at 298 K were observed in fields of 700 Oe. Corresponding field sensitivities as high as 170%/T at 3 mT and 298 K, and 700%–960%/T at 3–8 mT and 77 K were obtained. The low-field MR is associated with intergranular transport of spin-polarized electrons. It is found to be highly anisotropic. The phenomenon is discussed in terms of spin-polarized transport through two kinds of grain boundaries. These represent two extremes of grain-boundary environments. © 1999 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.123024

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