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  • 1
    Digitale Medien
    Digitale Medien
    Magnetic viscosity of single domain magnetite particles (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 5533-5537 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The acquisition of viscous magnetization has been measured on a single domain magnetite sample in the temperature range 80 to 330 K and in applied fields up to 1540 Oe. Based on Néel's single domain theory, we have calculated the field and temperature dependence of viscous acquisition by numerical two-dimensional integration, using experimentally determined volume and switching field distributions. Predicted and experimental viscosity coefficients do not match, with especially strong discrepancies below the Verwey transition. The experimental acquisition coefficient is larger below the transition than at room temperature, even though the corresponding switching field distributions are nearly identical. Thus we cannot explain single domain viscosity by switching field and volume distributions alone, and we suspect that stress plays a prominent role.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.350211
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  • 2
    Digitale Medien
    Digitale Medien
    Evidence for TRM domain wall moments? (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 102 (1990), S. 0 
    Details
    ISSN: 1365-246X
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: Multidomain ferro- and ferrimagnets carrying a thermoremanent magnetization (TRM) display a maximum in remanent magnetization just below the Curie temperature Tc when continuously demagnetized in zero field. We interpret this demagnetization peak to be indicative of the presence of TRM domain wall moments that grow in a small temperature interval (near Tc) upon heating where the domain wall volume increases at a rate faster than the decrease in spontaneous magnetization Msp. Hysteresis measurements in the vicinity of Tc on a single crystal of magnetite show that the spontaneous magnetization may be orders of magnitude smaller than the strong field magnetization measured in Ms/T curves. Micromagnetic calculations using experimentally determined Msp/T data suggest that the single domain (SD) threshold for magnetite can increase by more than an order of magnitude from room temperature to just below Tc in support of the domain wall moment model.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-246X.1990.tb04471.x
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  • 3
    Digitale Medien
    Digitale Medien
    Extinct spreading on the Cocos Ridge (1998)
    Oxford, UK : Blackwell Science Ltd
    Terra nova 10 (1998), S. 0 
    Details
    ISSN: 1365-3121
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: Using recently acquired marine magnetic data and existing magnetic and bathymetric data sets together with ODP Leg 170 age determinations we present a revised plate tectonic model for the southern Cocos and northern Nazca plate area. According to this model the formation of the southern Cocos plate was governed by spreading at different ridge axes with alternations between spreading ridges producing a complex magnetic anomaly pattern. In the Cocos and Malpelo ridge area we have identified two precursors of the recently active Cocos–Nacza spreading system which were active from 22.8 to 14.7 Ma, with a change in spreading direction from NW–SE to ENE–WSW at 19.5 Ma. The oceanic crust of these abandoned spreading systems was subsequently thickened and overprinted by hotspot volcanism that formed the Cocos and Malpelo ridges. The centre of this hotspot volcanism is about 500 km away from, but most probably related to, the Galapagos hotspot.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1365-3121.1998.00195.x
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  • 4
    Digitale Medien
    Digitale Medien
    Magnetic Susceptibility of Pyrrhotite: Grain Size, Field and Frequency Dependence (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 114 (1993), S. 0 
    Details
    ISSN: 1365-246X
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: The field and frequency dependences of the initial susceptibility of pyrrhotite have been analysed as a function of grain size, motivated by a strong field dependence recently observed for large (mm-sized) pyrrhotite crystals (Worm 1991) and smaller field dependences determined on smaller grain sizes by Clark (1984). In the present study, the frequency ranged from 30 Hz to 27 kHz. At 2 kHz, a field range from 0.05 to 1500 μT was investigated. Separate determinations of in-phase (K') and quadrature (k”) susceptibility components allow for the analysis of eddy current effects.Up to 4 kHz the in-phase susceptibility of a pyrrhotite-ore specimen is practically independent of frequency whereafter it decreases while the quadrature component increases linearly with frequency to a value on the order of k' at 20kHz for large grains. k” is proportional to d2μ where d is grain diameter, μ the intrinsic permeability, σ the electrical conductivity and f the frequency. the frequency response of magnetite is essentially flat up to frequencies 〉20 kHz. Both frequency dependences agree well with calculations based on the theory by Wait (1951). the conductivity of the pyrrhotite ore has been determined to be σ= 1.40 (±0.05). 105Ω−1m−1.The susceptibility of pyrrhotite and its field dependence increase strongly with grain size. While the susceptibility of grains smaller than 30 μm is field independent (up to 1.5 mT) it may increase as kα H0.25 for mm-sized crystals in fields 〉10μT. For most samples the Rayleigh law is inadequate to characterize induced magnetizations in weak alternating fields. When susceptibilities are measured for geomagnetic anomaly modelling, laboratory fields should be of similar intensity as the Earth's field and of frequency ≤1 kHz.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-246X.1993.tb01472.x
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  • 5
    Digitale Medien
    Digitale Medien
    Rock magnetism of pelagic sediments from the Equatorial Pacific
    Amsterdam : Elsevier
    Earth and Planetary Science Letters 89 (1988), S. 184-192 
    Details
    ISSN: 0012-821X
    Quelle: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Thema: Geologie und Paläontologie , Physik
    Materialart: Digitale Medien
    URL: http://linkinghub.elsevier.com/retrieve/pii/0012-821X(88)90171-9
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  • 6
    Digitale Medien
    Digitale Medien
    Domain size, closure domains, and the importance of magnetostriction in magnetite
    Amsterdam : Elsevier
    Earth and Planetary Science Letters 102 (1991), S. 71-78 
    Details
    ISSN: 0012-821X
    Quelle: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Thema: Geologie und Paläontologie , Physik
    Materialart: Digitale Medien
    URL: http://linkinghub.elsevier.com/retrieve/pii/0012-821X(91)90018-D
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  • 7
    Digitale Medien
    Digitale Medien
    The preparation of dispersed titanomagnetite particles by the glass-ceramic method
    Amsterdam : Elsevier
    Physics of the Earth and Planetary Interiors 46 (1987), S. 263-269 
    Details
    ISSN: 0031-9201
    Quelle: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Thema: Geologie und Paläontologie , Physik
    Materialart: Digitale Medien
    URL: http://linkinghub.elsevier.com/retrieve/pii/0031-9201(87)90189-0
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  • 8
    Digitale Medien
    Digitale Medien
    Fourier analysis of digital hysteresis data: rock magnetic applications
    Amsterdam : Elsevier
    Physics of the Earth and Planetary Interiors 65 (1990), S. 78-87 
    Details
    ISSN: 0031-9201
    Quelle: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Thema: Geologie und Paläontologie , Physik
    Materialart: Digitale Medien
    URL: http://linkinghub.elsevier.com/retrieve/pii/0031-9201(90)90077-B
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  • 9
    Digitale Medien
    Digitale Medien
    Magnetic hysteresis properties of fine particle titanomagnetites precipitated in a silicate matrix
    Amsterdam : Elsevier
    Physics of the Earth and Planetary Interiors 46 (1987), S. 84-92 
    Details
    ISSN: 0031-9201
    Quelle: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Thema: Geologie und Paläontologie , Physik
    Materialart: Digitale Medien
    URL: http://linkinghub.elsevier.com/retrieve/pii/0031-9201(87)90174-9
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  • 10
    Digitale Medien
    Digitale Medien
    Field dependence of magnetic anisotropy in pyrrhotite: effects of texture and grain shape
    Amsterdam : Elsevier
    Physics of the Earth and Planetary Interiors 76 (1993), S. 137-149 
    Details
    ISSN: 0031-9201
    Quelle: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Thema: Geologie und Paläontologie , Physik
    Materialart: Digitale Medien
    URL: http://linkinghub.elsevier.com/retrieve/pii/0031-9201(93)90063-F
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