Effect of the addition of Cr, Ta and Nb on structural and magnetic properties of Fe-Si alloys

High-resolution X-ray diffraction patterns of Fe78.5Si20Ta1.5 and Fe80−xSi20Nbx (x=0.5, 3.0, 10) show the existence of a metastable hexagonal phase (NbFe2−xSix and TaFe2−xSix) together with bcc-Fe100−ySiy solid solution and an amorphous matrix. The grain size of the bcc-Fe100−ySiy phase decreases with increasing Nb content in Fe-Si compounds resulting in nanocrystalline materials. On the other side, the micro-strain, the lattice constant, coercivity and the Curie temperature increase with Nb concentration. Enhancements of the local strain and local magnetic anisotropy were also observed by means of NMR measurements. On the contrary, the addition of Cr causes a decrease in the coercivity and Curie temperature.