Structure and magnetic properties of vacuum- and air-annealed rapidly quenched Mo- and Co-modified Fe85.3Cu0.7B14 alloy

In the present work, comprehensive structural and magnetic studies of the vacuum- and air-annealed, followed by rapid quenching Fe85.3Cu0.7B14 ribbons, modified by Co and Mo, have been reported. Three different alloys, i.e. Fe80.3Co5Cu0.7B14, Fe80.3Mo5Cu0.7B14, and Fe75.3Co5Mo5Cu0.7B14, were first produced in the pure amorphous state via melt-spinning technique and then characterised by X-ray diffraction and differential scanning calorimetry methods. Based on these results, the annealing process has been optimised in the temperature range between 280 and 540 °C towards improving the magnetic properties (saturation induction (Bs), coercivity (Hc), core power losses at 1 T and 50 Hz (P10/50)). For the optimal conditions (at the minimum value of P10/50), the complex permeability in the 104–108 Hz frequency range, together with the core power losses obtained from magnetic induction dependence up to the frequency of 400 kHz, was successfully measured. The local and average crystal structures were investigated by the X-ray and neutron diffraction complemented by transmission electron microscopy observations proving for Fe80.3Co5Cu0.7B14 alloy, the nanocrystalline phase embedded in the glassy matrix, however with the crystal growth rate restricted to only an early stage of crystallisation. In addition, better magnetic parameters of Fe80.3Co5Cu0.7B14 alloy were obtained for optimal air-annealing conditions than those of the vacuum-annealed sample. The chemical composition mapping along the air-annealed ribbon cross-section indicated an oxygen-rich layer with a thickness of about 140 nm. As shown, oxygenation has a positive impact on magnetic properties. Finally, the vacuum- and air-annealed alloys have been characterised using 57Fe Mössbauer spectrometry and transmission electron microscopy.