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2 Apr 2001

Volume 78, Issue 14, pp. 1961-2084

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Discovery of magnetite in the exhausted material from a diesel engine

W. Abdul-Razzaq and M. Gautam

Appl. Phys. Lett. 78, 2018 (2001); http://dx.doi.org/10.1063/1.1358357 (2 pages) | Cited 11 times

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Magnetite was detected in the particulate matter collected from diesel engine exhaust using a total exhaust dilution tunnel. This discovery is very important in determining the health effects of exposure to magnetite or its interaction with static magnetic fields or low-frequency electromagnetic fields. Magnetite is the best absorber of microwave radiation of any biological material in the 0.5–10 GHz frequency range through the process of electromagnetic resonance. This includes the frequencies that are normally used in the cellular telephone industry. © 2001 American Institute of Physics.
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89.60.-k Environmental studies
92.60.Sz Air quality and air pollution
78.70.Gq Microwave and radio-frequency interactions

Magnetization reversal and coercivity of a single-domain Co/Pt dot measured with a calibrated magnetic force microscope tip

J. Lohau, A. Carl, S. Kirsch, and E. F. Wassermann

Appl. Phys. Lett. 78, 2020 (2001); http://dx.doi.org/10.1063/1.1361100 (3 pages) | Cited 14 times

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The magnetization reversal and the coercivity of a nanofabricated single-domain 230 nm diam Co/Pt multilayer dot with perpendicular magnetic anisotropy are measured quantitatively with magnetic force microscopy (MFM). During MFM imaging, a variable external magnetic field ranging between −1 kOe<H<1 kOe is applied in the z direction in order to simultaneously reverse the magnetizations of both the single-domain Co/Pt dot and the MFM tip. The hysteresis loop of the Co/Pt dot can be extracted unambiguously from the resulting MFM image contrast, since we have used a calibrated MFM tip, for which the magnetization reversal has been determined independently also by MFM using a nanofabricated current carrying ring. © 2001 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.75.-c Magnetic properties of nanostructures
75.60.Jk Magnetization reversal mechanisms
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy

Anisotropic magnetic domain structure of layered manganite La1.4Sr1.6Mn2O7

T. Fukumura, T. Hasegawa, H. Sugawara, K. Tanaka, H. Sakaki, T. Kimura, and Y. Tokura

Appl. Phys. Lett. 78, 2023 (2001); http://dx.doi.org/10.1063/1.1359778 (3 pages) | Cited 2 times

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The anisotropic magnetic domain structure of a layered manganite La1.4Sr1.6Mn2O7 has been analyzed quantitatively. The evaluated dimensions of the domain indicate the low dimensionality and reproduce spontaneous formation of the bubble domain taking stability of the bubble domain into account. The ferromagnetic regions observed below the Neel temperature might be responsible for the limited tunneling magnetoresistance ratio reported in this compound. © 2001 American Institute of Physics.
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75.60.Ch Domain walls and domain structure
75.30.Gw Magnetic anisotropy
75.50.Ee Antiferromagnetics
75.50.Cc Other ferromagnetic metals and alloys
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.47.Gk Colossal magnetoresistance

Temperature-dependent magnetoresistance of magnetic tunnel junctions with ultraviolet light-assisted oxidized barriers

U. May, K. Samm, H. Kittur, J. Hauch, R. Calarco, U. Rüdiger, and G. Güntherodt

Appl. Phys. Lett. 78, 2026 (2001); http://dx.doi.org/10.1063/1.1361098 (3 pages) | Cited 14 times

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Co(10 nm)/AlOx(nominally 2 nm)/Co(20 nm) tunnel junctions have been prepared under ultrahigh vacuum conditions applying a shadow mask technique. An ultraviolet light-assisted oxidation process of the AlOx barrier has been optimized by in situ x-ray photoelectron spectroscopy, in conjunction with temperature-dependent tunneling magnetoresistance measurements. Optimum-oxidized tunnel junctions show a magnetoresistance of 20% at 285 K, and up to 38% at 100 K. For under-oxidized samples, with a remaining Al layer between the Co bottom electrode and the AlOx barrier, the tunneling magnetoresistance decreases more rapidly with increasing temperature than observed for the over-oxidized samples. The resistance × area product of optimum-oxidized tunneling junctions exhibits a minimum, and increases for under- and over-oxidized samples. © 2001 American Institute of Physics.
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81.65.Mq Oxidation
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.40.Gk Tunneling
73.61.At Metal and metallic alloys

Current-driven reversal in annular vertical giant magnetoresistive devices

K. Bussmann, G. A. Prinz, R. Bass, and J.-G. Zhu

Appl. Phys. Lett. 78, 2029 (2001); http://dx.doi.org/10.1063/1.1353819 (2 pages) | Cited 15 times

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Experiments are reported that demonstrate the asymmetric switching behavior reported earlier in vertical giant magnetoresistance devices arises from the solid disk geometry of the device that produces a magnetic singularity at the disk center. Annular devices having a 0.1 μm center hole and 0.5 μm outer diameter are shown to switch symmetrically with an Amperian field. © 2001 American Institute of Physics.
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85.75.Bb Magnetic memory using giant magnetoresistance
75.47.De Giant magnetoresistance
75.60.Jk Magnetization reversal mechanisms
75.75.-c Magnetic properties of nanostructures

Critical current density of YBa2Cu3O7−δ low-angle grain boundaries in self-field

D. T. Verebelyi, C. Cantoni, J. D. Budai, D. K. Christen, H. J. Kim, and J. R. Thompson

Appl. Phys. Lett. 78, 2031 (2001); http://dx.doi.org/10.1063/1.1360230 (3 pages) | Cited 24 times

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A study has been perfomed on the superconducting critical current density Jc flowing across low-angle grain boundaries in epitaxial thin films of YBa2Cu3O7−δ. The materials studied were dual grain boundary rings deposited on SrTiO3 and containing 2°, 3°, 5°, and 7° tilt boundaries. The current density in self-field was determined by magnetometric methods at temperatures from 5 K to Tc. We conclude that at the higher temperatures of coated conductor applications, there is limited potential for improving Jc by reducing the grain boundary angle below ∼ 3°. © 2001 American Institute of Physics.
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74.25.Sv Critical currents
74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
61.72.Mm Grain and twin boundaries
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