  Artificial tuning of dielectric parameters can result from interface
conductivity in polycrystalline materials. In ferroelectric single crystals, it
was already shown that ferroelectric domain walls can be the source of such
artificial coupling. We show here that low temperature dielectric losses can be
tuned by a dc magnetic field. Since such losses were previously ascribed to
polaron relaxation we suggest this results from the interaction of hopping
polarons with the magnetic field. The fact that this losses alteration has no
counterpart on the real part of the dielectric permittivity confirms that no
interface is to be involved in this purely dynamical effect. The contribution
of mobile charges hopping among Fe related centers was confirmed by ESR
spectroscopy showing maximum intensity at ca T\sim40 K.
