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| Titel |
Quantification of magnetic nanoparticles with broadband measurements of magnetic susceptibility in the frequency domain |
| VerfasserIn |
Kazuto Kodama, Zhisheng An, Hong Chang, XiaoKe Qiang |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250105292
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| Publikation (Nr.) |
 EGU/EGU2015-4789.pdf |
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| Zusammenfassung |
| Measurement of low-field magnetic susceptibility over a wide band of frequencies spanning
four orders of magnitude is a useful method for the assessment of the grain size distribution
of ultrafine magnetic particles smaller than the SP/SSD boundary. This method has been
applied to a loess/paleosol sequence at Luochuan in the Chinese Loess Plateau. The studied
succession consists of sequences from the latest paleosol unit to the upper part of the loess
unit, spanning the last glacial–interglacial cycle. Reconstructed grain size distributions
(GSDs) consist of volume fractions on the order of 10-24 m3, and the mean GSDs are
modal but with distinctive skewness among the loess, the weakly developed paleosol
(weak paleosol), and the mature paleosol. This indicates that the mean volume of SP
particles in this sequence tends to increase during the transition from the loess to the
paleosol. An index, defined as the difference between Ï130 at the lowest (130 Hz)
and Ï500k at the highest (500 kHz) frequencies normalized to Ï130, is judged to
be a more suitable index than previous frequency dependence parameters for the
concentration of SP particles. This index has a strong correlation with Ï130, showing a
continuous ‘growth curve’ with the rate of increase being highest for the loess,
moderate for the weak paleosol, and saturated for the paleosol. The characteristic
curve suggests that smaller SP particles are preferentially formed in the earlier stage
of pedogenesis rather than the later phase when even larger particles are formed
in the mature paleosol. These results demonstrate that the broad-band-frequency
susceptibility measurement will be useful for the quantitative assessment of magnetic
nanoparticles in soils and sediments. Additionally, we point out that the measurement in the
frequency domain generally requires time and may not be most suitable to routine
measurements. We thus propose an alternative manner, the measurement in the
time domain that can be performed by measurement of transient magnetization
induced by a pulsed field. Results from preliminary measurements, coupled with
simulation based on the linear response theory, suggest that the transient response
in the time domain can be converted into the spectrum in the frequency domain. |
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