Magnetic properties of a recent parabrown-earth from Southern Germany

We report here the analysis of the magnetic properties of a para-brown earth from Southern Germany. Susceptibility, isothermal remanence, ratio of anhysteretic to isothermal remanence, various hysteresis parameters and viscous remanence were measured. In addition, some standard pedological parameters were determined: pH value, content of organic carbon and content of iron (hydr)oxides. For the characterization of the magnetic particles, scanning and transmission electron microscope observations were employed. We found that it is possible to define a vertical structure in the soil by magnetic measurements and that it reveals details not seen in the general pedological horizons. Magnetic properties in the topsoil were influenced by the former cultivation of the soil and by the presence of a remarkable amount of strongly magnetic industrial fly ash. In the underlying horizons pedogenically formed ferrimagnetic minerals dominate the magnetic properties. We could prove that this material forms only in the presence of iron-reducing bacteria. Transmission electron microscopy showed that these magnetite particles have an average grain size of 5 nm. We suggest that these grains form clusters as the magnetic properties rather indicate particles that are at the boundary between superparamagnetic and single domain behavior.