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Studia Geophysica et Geodaetica

, Volume 56, Issue 3, pp 803–825 | Cite as

Frequency-dependent susceptibility and other magnetic properties of Celtic and Mediaeval graphitic pottery from Bohemia: an introductory study

  • Marta Chlupáčová
  • František Hrouda
  • Daniel Nižňanský
  • Václav Procházka
  • Zdeňka Petáková
  • František Laufek
Article

Abstract

Frequency-dependent magnetic susceptibility, its anisotropy (AMS), its temperature variation, natural remanent magnetization and time-dependent isothermal remanent magnetization as well as Mössbauer spectroscopy of a small collection of Celtic and Mediaeval graphitic pottery from Southern Bohemia were investigated. The mineral composition of the pottery is dominated by fragments of quartz, accompanied mainly by various silicates from granitoids and paragneisses, or by calcite, within the plastic component being probably illite but also graphite. No ferrimagnetic minerals were found in optical microscope, among Fe-oxides only limonite was observed, even though the bulk susceptibility of the pottery varies in the orders of 10−4 to 10−2 [SI]. This may indicate presence of ferromagnetic particles in the ultrafine (superparamagnetic, SP) state, which is confirmed by frequency-dependent susceptibility ranging from 3% to almost 16%. The low temperature susceptibility vs. temperature curves are only moderately sloped, showing the Verwey transition only in one case. The high temperature curves mostly show presence of two magnetic phases, maghemite and magnetite. Cooling curves show distinctly lower susceptibilities than the heating curves indicating instability of the assemblage of ferrimagnetic minerals, particularly in temperatures slightly under 700 °C. Mössbauer spectroscopy confirmed the results of the frequency-dependent susceptibility, showing the increase of ferrimagnetic sextets in the spectra measured at 4.2K, likely indicating maghemite as the distinct ferrimagnetic phase. The frequency-dependent AMS indicates preferred orientation of SP1,16 particles, coaxiality between SP1,16 grain AMS and whole specimen AMS indicate that all grains, ultrafine and coarser ones, were oriented by the same process, i.e. copying the pottery structure created during wheel-turning.

Keywords

magnetic properties Celtic and Mediaeval graphitic pottery superparamagnetic particles 

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Copyright information

© Institute of Geophysics of the ASCR, v.v.i 2012

Authors and Affiliations

  • Marta Chlupáčová
    • 1
  • František Hrouda
    • 2
    • 3
  • Daniel Nižňanský
    • 4
  • Václav Procházka
    • 5
  • Zdeňka Petáková
    • 6
  • František Laufek
    • 6
  1. 1.Boháčova 866/4Praha 4Czech Republic
  2. 2.AGICO Ltd.BrnoCzech Republic
  3. 3.Institute of Petrology and Structural GeologyCharles UniversityPraha 2Czech Republic
  4. 4.Institute of Inorganic ChemistryCharles UniversityPraha 2Czech Republic
  5. 5.Institute of Chemical TechologyPraha 6Czech Republic
  6. 6.Czech Geological SurveyPrahaCzech Republic

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