  In this work, we report the thermal characterization of platelike composite
samples made of polyester resin and magnetite inclusions. By means of
photoacoustic spectroscopy and thermal relaxation, the thermal diffusivity,
conductivity and volumetric heat capacity of the samples were experimentally
measured. The volume fraction of inclusions was systematically varied in order
to study the changes in the effective thermal conductivity of the composites.
In some samples, a static magnetic field was applied during the polymerization
process resulting in anisotropic inclusion distributions. Our results show a
decrease in the thermal conductivity of some of the anisotropic samples
compared to the isotropic randomly distributed ones. Our analysis indicates
that the development of elongated inclusion structures leads to the formation
of magnetite and resin domains causing this effect. We correlate the complexity
of the inclusion structure with the observed thermal response by a multifractal
and lacunarity analysis. All the experimental data are contrasted with the well
known Maxwell-Garnett's effective media approximation for composite materials.
