Magnetic and crystalline structure as well as magnetic and damping properties of binary iron-aluminum (Fe-Al) alloys in the region from 3 to 12 wt.% aluminum have been investigated by using transmission electron microscopy (TEM), X-ray scattering, neutron scattering, magnetic hysteresis loops, and magnetostriction studies.
It was found that independent of the impurity content (vacuum or air melting of alloys) the concentration dependence of damping capacity displays a pronounced maximum in the region of ̃5.5 wt.% aluminum, where the maximum value of the logarithmic decrement δ exceeds 25%. It was found that the magnetic domain structures in the bulk materials differ strongly for the alloys in the high damping state and for the alloys with the same composition after suppressing the high damping by heat treatment.
The analysis of obtained magnetic data and microstructural analysis shows that the necessary condition for the appearance of the high damping state is the formation of a special magnetic domain structure with an enhanced fraction of movable 90-deg domain walls. An additional condition is the formation of a crystalline structure which provides a moderate value of magnetic hysteresis losses and coercive force. For the Fe-Al alloys investigated, it means that the most favorable structural condition for high δ-values is an intermediate stage of short-range ordering of the D03 structure.