Microwave permeability of nanocrystalline alloys (Fe0.67Co0.33)78Nb6B15Cu1 and (Fe0.67Co0.33)78Nb6Al6B9Cu1

Amorphous alloys (Fe0.67Co0.33)78Nb6B15Cu1 and (Fe0.67Co0.33)78Nb6Al6B9Cu1 have been prepared by a rapid quench method. Subsequent heat treatments at a temperature between the primary and secondary crystallization temperature give rise to the coexistence of two ferromagnetic phases: amorphous matrix and nanocrystalline grains (α′α′-FeCo). Microwave permeability of flaky particles have been measured within 1–18 GHz. Fitting based on the revised Kittel’s law has uncoupled the effects of two ferromagnetic phases on the microwave permeability via the natural resonance mechanism. Due to its lower magnetic anisotropy field, the amorphous matrix has lower natural resonance frequency than that of α′α′-FeCo nano grains. Besides, it is found that partial substitution B with Al can effectively abate surface oxidation, but which reduce the saturation magnetization and slightly increase the coercivity and resonance frequencies of both ferromagnetic phases.

► Magnetic flakes have been fabricated by milling the magnetic ribbons.
► Partial substitution B with Al can abate surface oxidation of HITPERM alloys.
► Revised Kittel law have been proposed to decompose the permeability dispersion spectra.
► The GHz permeability dispersion strongly depends on the nanocrystalline phase.