In this article, we report a detailed study of the paramagnetic susceptibility χ of Sr2FeMoO6ceramic samples prepared under various conditions. We show that χ-1(T, H) has a rather unconventional behavior in the 800K>T>7C(≈400 K) temperature range, namely, a field-dependent χ-1(T) slope which is also sensitive to the synthesis conditions. Detailed analysis and comparison of samples allow us to conclude that this behavior is nonintrinsic but rather reflects the sample quality. We quantitatively show that small amounts of ferromagnetic impurities (<0.1%) can account for the observed behavior. In spite of this, we demonstrate that the dominant magnetic interactions in this system are ferromagnetic, thus strongly supporting a double-exchange mechanism for magnetic interactions. © 2001 American Institute of Physics.