A comprehensive study of the magnetic properties of baked clays containing ferrimagnetic
particles in various magnetic states, including superparamagnetic, has been carried out
in this work. The phase composition of the magnetic fraction of laboratory and industrial
samples made from the same clay is mainly represented by iron (III) oxide polymorphs and
possibly non-stoichiometric magnetite. Experimental methods included magnetic granulometry, Mössbauer spectroscopy, scanning electron microscopy, X-ray phase analysis, and
pulsed electromagnetic measurements. A theoretical model of magnetostatically interacting
particles with a lognormal volume distribution was used to interpret the experimental data,
allowing the contribution of superparamagnetic grains to be taken into consideration. It
is shown that the firing mode significantly affects the composition of iron oxide phases
and their magnetic characteristics. Laboratory samples are characterized by approximately
twice the proportion of superparamagnetic particles. At sufficiently low concentrations of
ferrimagnet in samples <0.1%, the concentration of superparamagnetic particles is even two
orders of magnitude lower. It is the use of pulse methods that provides a more reliable diagnosis of their presence. The complex application of experimental methods with theoretical
modeling makes it possible to reveal and quantitatively describe the microheterogeneous
nature of the magnetic state of baked clays, which is applicable to a wide range of magnetic
materials, and to analyze more deeply the thermal and phase history of archaeological and
geological objects.