[en] The controlled crystallization of a Finemet-type amorphous alloy to a nanocrystalline state leads to a known increase in the permeability μ and an immense reduction in its disaccommodation DA. We have found that the maximum of μ is split, and DA changes sign to negative in the corresponding fields irrespective of their shift with frequency. The direct observation of magnetic domain structure in a 1 kHz field revealed an irreversible change in the equilibrium position of the wall in the same field region. We suggest that all three phenomena are connected to stabilization and destabilization of the domain walls. ((orig.))