Role of P in Nanocrystallization of ${\rm Fe}_{85}{\rm Si}_{2}{\rm B}_{8}{\rm P}_{4}{\rm Cu}_{1}$

The role of P in the nanocrystallization of a newly developed Fe-based Fe₈₅Si₂B₈P₄Cu₁ soft magnet (NANOMET) is investigated by differential scanning calorimetry (DSC), high-energy X-ray diffraction (XRD), and transmission electron microscope. DSC results show that addition of P into Fe₈₅Si₂B₈P₄Cu₁ retards growth of α-Fe precipitates and also hinders the onset of crystallization of the residual amorphous phase. High-energy XRD results indicate that a lattice parameter of the precipitated α-Fe is 2.86652 Å, which is very close to that of pure bcc Fe. A small amount of P and/or Si, however, are resolved in nanocrystalline Fe, which causes Curie temperature (TC) of the precipitated α-Fe to decrease by ΔT_C = 31 K lower than the value of pure bcc Fe. With increase in the volume fraction of the precipitated α-Fe, the concentration of residual amorphous becomes close to that of the most stable amorphous alloy, i.e., Fe₇₆Si₉B₁₀P₅ when the volume fraction approaches to 40%. P in NANOMET contributes to hinder the formation of Fe-B(Si,P) compounds by stabilizing residual amorphous phase.