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Dimo Dimov – One of the best experts on this subject based on the ideXlab platform.

  • Changes in mean magnetic susceptibility and its anisotropy of rock samples as a result of Alternating Field demagnetization
    Earth and Planetary Science Letters, 2007
    Co-Authors: Diana Jordanova, Neli Jordanova, Bernard Henry, Jozef Hus, Jérôme Bascou, Minoru Funaki, Dimo Dimov

    Abstract:

    Measurements of low-Field magnetic susceptibility (K) and its anisotropy (AMS) on different rock types during stepwise Alternating Field (AF) demagnetization in increasing Fields revealed not only significant changes of the AMS principal susceptibilities, but also an increase of the mean magnetic susceptibility (Km). Studied collections of loess/paleosol samples from different sections in Belgium, Bulgaria, China, Siberia and Tadjikistan and diorites, granites and gneisses from Antarctica show systematic Km-increase, between 2 and 27% as compared to the initial values, after AF-demagnetization up to 100 or 200 mT maximum amplitude. The relationships between magnetic susceptibility increase and magnetic hysteresis parameters and their ratios, indicate that the Km-increase is due to changes in magnetic domain configuration of the initial natural remanent magnetization (NRM) state of the remanence carriers during AF-treatment. The obtained linear relationship between K-increase and the degree of anisotropy P′ for strongly anisotropic gneiss samples suggests that magnetostatic interactions also play a role in the observed AF-effect on Km.

  • Changes in mean magnetic susceptibility and its anisotropy of rock samples as a result of Alternating Field demagnetization
    Earth and Planetary Science Letters, 2007
    Co-Authors: Diana Jordanova, Neli Jordanova, Bernard Henry, Jozef Hus, Jérôme Bascou, Minoru Funaki, Dimo Dimov

    Abstract:

    International audienceMeasurements of low-Field magnetic susceptibility (K) and its anisotropy (AMS) on different rock types during stepwise Alternating Field (AF) demagnetization in increasing Fields revealed not only significant changes of the AMS principal susceptibilities, but also an increase of the mean magnetic susceptibility (Km). Studied collections of loess/paleosol samples from different sections in Belgium, Bulgaria, China, Siberia and Tadjikistan and diorites, granites and gneisses from Antarctica show systematic Km-increase, between 2 and 27% as compared to the initial values, after AF-demagnetization up to 100 or 200 mT maximum amplitude. The relationships between magnetic susceptibility increase and magnetic hysteresis parameters and their ratios, indicate that the Km-increase is due to changes in magnetic domain configuration of the initial natural remanent magnetization (NRM) state of the remanence carriers during AF-treatment. The obtained linear relationship between K-increase and the degree of anisotropy P′ for strongly anisotropic gneiss samples suggests that magnetostatic interactions also play a role in the observed AF-effect on Km

  • Alternating Field-impressed AMS in rocks
    Geophysical Journal International, 2007
    Co-Authors: Bernard Henry, Diana Jordanova, Neli Jordanova, Jozef Hus, Jérôme Bascou, Minoru Funaki, Dimo Dimov

    Abstract:

    We studied the evolution of anisotropy of magnetic susceptibility (AMS) during stepwise Alternating Fields (AF) demagnetization on various kinds of rock samples (loess and palaeosols, diorite, granite, gneiss) with very different degree of magnetic anisotropy. The variation of the magnetic fabric appears to be related to both the magnetic fabric before AF demagnetization and to the direction of AF application. The anisotropy change is mainly controlled by the initial magnetic fabric. The more anisotropic is the initial magnetic fabric, the less is the effect of the direction of Field application. This can be clearly shown by determination of the difference of the susceptibility ellipsoids after and before AF application. Even for rocks with weak magnetic anisotropy, the effect of the initial AMS is significant. The difference ellipsoids allow in particular cases to point out that the initial magnetic fabric is composite.

Diana Jordanova – One of the best experts on this subject based on the ideXlab platform.

  • Changes in mean magnetic susceptibility and its anisotropy of rock samples as a result of Alternating Field demagnetization
    Earth and Planetary Science Letters, 2007
    Co-Authors: Diana Jordanova, Neli Jordanova, Bernard Henry, Jozef Hus, Jérôme Bascou, Minoru Funaki, Dimo Dimov

    Abstract:

    Measurements of low-Field magnetic susceptibility (K) and its anisotropy (AMS) on different rock types during stepwise Alternating Field (AF) demagnetization in increasing Fields revealed not only significant changes of the AMS principal susceptibilities, but also an increase of the mean magnetic susceptibility (Km). Studied collections of loess/paleosol samples from different sections in Belgium, Bulgaria, China, Siberia and Tadjikistan and diorites, granites and gneisses from Antarctica show systematic Km-increase, between 2 and 27% as compared to the initial values, after AF-demagnetization up to 100 or 200 mT maximum amplitude. The relationships between magnetic susceptibility increase and magnetic hysteresis parameters and their ratios, indicate that the Km-increase is due to changes in magnetic domain configuration of the initial natural remanent magnetization (NRM) state of the remanence carriers during AF-treatment. The obtained linear relationship between K-increase and the degree of anisotropy P′ for strongly anisotropic gneiss samples suggests that magnetostatic interactions also play a role in the observed AF-effect on Km.

  • Changes in mean magnetic susceptibility and its anisotropy of rock samples as a result of Alternating Field demagnetization
    Earth and Planetary Science Letters, 2007
    Co-Authors: Diana Jordanova, Neli Jordanova, Bernard Henry, Jozef Hus, Jérôme Bascou, Minoru Funaki, Dimo Dimov

    Abstract:

    International audienceMeasurements of low-Field magnetic susceptibility (K) and its anisotropy (AMS) on different rock types during stepwise Alternating Field (AF) demagnetization in increasing Fields revealed not only significant changes of the AMS principal susceptibilities, but also an increase of the mean magnetic susceptibility (Km). Studied collections of loess/paleosol samples from different sections in Belgium, Bulgaria, China, Siberia and Tadjikistan and diorites, granites and gneisses from Antarctica show systematic Km-increase, between 2 and 27% as compared to the initial values, after AF-demagnetization up to 100 or 200 mT maximum amplitude. The relationships between magnetic susceptibility increase and magnetic hysteresis parameters and their ratios, indicate that the Km-increase is due to changes in magnetic domain configuration of the initial natural remanent magnetization (NRM) state of the remanence carriers during AF-treatment. The obtained linear relationship between K-increase and the degree of anisotropy P′ for strongly anisotropic gneiss samples suggests that magnetostatic interactions also play a role in the observed AF-effect on Km

  • Alternating Field-impressed AMS in rocks
    Geophysical Journal International, 2007
    Co-Authors: Bernard Henry, Diana Jordanova, Neli Jordanova, Jozef Hus, Jérôme Bascou, Minoru Funaki, Dimo Dimov

    Abstract:

    We studied the evolution of anisotropy of magnetic susceptibility (AMS) during stepwise Alternating Fields (AF) demagnetization on various kinds of rock samples (loess and palaeosols, diorite, granite, gneiss) with very different degree of magnetic anisotropy. The variation of the magnetic fabric appears to be related to both the magnetic fabric before AF demagnetization and to the direction of AF application. The anisotropy change is mainly controlled by the initial magnetic fabric. The more anisotropic is the initial magnetic fabric, the less is the effect of the direction of Field application. This can be clearly shown by determination of the difference of the susceptibility ellipsoids after and before AF application. Even for rocks with weak magnetic anisotropy, the effect of the initial AMS is significant. The difference ellipsoids allow in particular cases to point out that the initial magnetic fabric is composite.

Robert S. Coe – One of the best experts on this subject based on the ideXlab platform.

  • A new protocol for three‐axis static Alternating Field demagnetization of rocks
    Geochemistry Geophysics Geosystems, 2016
    Co-Authors: David Finn, Robert S. Coe

    Abstract:

    Static three-axis Alternating Field (AF) demagnetization is the most common method regularly implemented for removing magnetic components of rock samples. This method is so widely used that one of its main limitations, the acquisition of gyroremanence (GRM), is often not accounted for or even discussed. The presence of GRM likely interferes more than is recognized in accurate determination of the most stable remanence. The accepted method proposed by Dankers and Zijderveld (1981) for excluding GRM affected measurements requires nearly triple the amount of lab work, and by consequence, is almost never regularly implemented on large batches of samples. Here, we present a laboratory procedure and subsequent analysis (SI method) that removes the effects of GRM in static AF demagnetization without requiring extra laboratory work. This paper, therefore, describes a new standard protocol for efficient static AF demagnetization of rocks.

  • Development of a 0.5 T magnetic‐core AlternatingField demagnetizer
    Geochemistry Geophysics Geosystems, 2016
    Co-Authors: W. E. Schillinger, E. R. Morris, Robert S. Coe, D. R. Finn

    Abstract:

    We have constructed an AlternatingField (AF) demagnetizer with a magnetic core in a passively air-cooled coil that can routinely operate at Fields up to 0.5 T, almost 3 times higher than we could attain before in our commercial instrument. The Field is powered by a commercial 1 kW power amplifier and is transverse to the bore, uniform to ±2% over a 25 mm paleomagnetic sample, and compatible with our existing sample handler for automated demagnetization and measurement. Even harmonics are ≤1 ppm of the fundamental and so generate negligible anhysteretic remanence. The much higher peak Alternating Field, 2 and 5 times that commonly available in air-core solenoidal and Helmhotz coil configurations, respectively, enables successful AF demagnetization of many samples that could not be completely demagnetized with commercially available equipment. This capability is especially useful for high-coercivity sedimentary and igneous rocks and extraterrestrial materials that contain magnetic minerals that alter during thermal demagnetization. In addition to the benefits, this instrument brings to our own research, a much broader potential impact is that it could replace the transverse coils of most automated AF demagnetization systems in use today, whether for discrete or continuous U-channel measurements, which are commonly limited to peak Fields of ∼100 mT. Manual and tumbling demagnetizers would benefit as well by the ∼2 times increase in maximum Field over those that can be attained by commercial solenoidal coils. Furthermore, we expect that it and similarly designed magnetic-core instruments will be capable of attaining even higher Fields, of order 1 T.