The effect of phosphorous on the microstructure and magnetic properties of as-spun and flash annealed (389–535 °C for 7 s) Fe85Cu1Si2B8P4 melt spun ribbons were investigated by three-dimensional atom probe (3DAP) and high resolution transmission electron microscopy (HRTEM) techniques. The formation of quasi-amorphous αα-Fe clusters of 3–5 nm size in an amorphous matrix were detected by HRTEM, despite the high quenching rate applied by high wheel speed used. Flash annealing of the as-spun ribbons gave rise to the formation of nanocrystalline αα-Fe (Si) phase in amorphous matrix containing Fe, Si, B and P elements as detected by 3DAP. Comparing 3DAP analysis of the samples annealed at 445 °C and 535 °C revealed that the concentration of P and B in amorphous matrix were increased for the latter. Further, it was shown that P hardly solidified into nanocrystalline phase and partitioned in amorphous phase alongside B atoms leading to the further stabilization of amorphous matrix as confirmed by 3DAP analysis. The highest magnitude of saturation magnetic induction (Bs~1.85 T) and the lowest coercive field (~10–20 A/m) were obtained for the samples annealed above 445 °C, for which noticeable reduction of saturation magnetostriction (λλs) were also detected.

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