Atomic Ordering of Soft Magnetic Fe–Si Alloys and Effect of Thermomagnetic Treatment

Abstract

A mechanism of isotropic improvement of magnetic properties of soft magnetic Fe–Si alloys with a bcc crystal lattice upon thermomagnetic treatment in an ac magnetic field is proposed. The essence of the mechanism is the applied alternating-sign magnetic field, which reorients axes of neighboring Si atoms pairs (“directed atomic ordering”) in nanoclusters with the FeSi (В2 type) superstructure and transfers the silicon atoms from the stable equilibrium position at centers of cubic cells into nonequilibrium position. In this case, bonding forces between atoms weaken, and the possibility of their displacement by moving magnetic-domain walls appears. As a result, nanoclusters are destroyed, and the redistribution of weakly coupled silicon atoms over the volume and isotropic improvement of magnetic properties of Fe—Si alloys occur. The dependence of the effect of thermomagnetic treatment of the Fe–Si alloys on the strength of applied dc magnetic field is explained (the effect of thermomagnetic treatment in low and high magnetic fields is anisotropic and isotropic, respectively).