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In this work we present frequency-dependent magnetic susceptibility and dc electric transport properties of three different compositions of hexaferrite Ba 1−x -Pb x Fe 12−y Al y O 19 . We find a correlation between activation energies of dc electric transport and ac magnetic susceptibility which persists in the whole researched range of aluminium substitution x = 0 to 3.3. This result is discussed in the context of charged magnetic domain walls, the pinning of which is determined by charge carriers activated over the transport gap. Our work points toward a general relaxational mechanism in ferrimagnetic semiconductors which directly affects dynamic magnetic properties via electric transport.