B2 and D03 clusters in soft magnetic single crystal Fe1-xSix alloys with induced magnetic anisotropy

The atomic structure of α-Fe1-xSix single crystals with x=0.05, 0.06, and 0.08 was studied by means of X-ray diffraction to clarify the origin of the magnetic anisotropy induced under thermomagnetic or thermomechanical treatment. The B2-type short-range order is observed only at x=0.05 and 0.06. B2 clusters, about 8A in size, are extended in the direction of induced magnetic anisotropy by ∼2A more than in a direction transverse to it. When the sequential junction of B2 unit cells-two or more in number-is realized along the easy magnetization axes <100>, the B2 clusters are inevitably anisotropic. The probability of the orientation of B2 clusters along any of the axes <100> is the same. The appeared preferable orientation of B2 clusters upon annealing in a dc saturating magnetic field or under stress loading has emerged via the Si-atom diffusion. After cooling, this anisotropic B2-cluster distribution becomes 'frozen' and is the origin of the appearance and stability of the uniaxial anisotropy of magnetic properties. In Fe0.92Si0.08, the B2 clusters coexist with D03 clusters, the latter being isotropic. With increasing x, the increase in a D03-phase amount progressively suppresses the magnetic anisotropy caused by anisotropic distribution of B2 clusters, and, to be exact, completely, at x∼0.14