LAUSR

Abstract The magnetic properties of nanocrystalline Fe77Si10B9Cu1Nb3-xAlx (x = 0 and 1) alloys have been investigated and their structural and electromagnetic parameters have been quantitatively studied by X-ray diffraction, transmission electron microscopy and Mossbauer spectra under one-step and two-step annealing processes. The nanocrystalline structure consists of single α-Fe(Si) phase embedded in a residual amorphous phase. Both saturation magnetic flux density (Bs) and permeability (μ) of the nanocrystalline alloys are increased by substituting 1 at% Al for Nb and one-step annealing, from Bs = 1.41 T to 1.47 T and from μ = 18,000 to 23,000 at 1 kHz, respectively. The two-step annealing has little effect on the Bs, coercivity (Hc) and grain size of the nanocrystalline alloys, but greatly improves the μ of the Al-doped alloy, reaching up to 28,000 at 1 kHz. The improved μ can be attributed to the increased magnetic moment and exchange stiffness constant, homogeneous chemical structure and reduced magnetostriction. The Al-doped nanocrystalline alloy with high Bs, high μ, low Hc and good frequency stability are good candidates for magnetic shielding pieces of wireless charging.