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
${\rm Fe}_{85}{\rm Si}_{{2}}{\rm B}_{{8}}{\rm P}_{{4}}{\rm Cu}_{{1}}$
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
${\rm Fe}_{85}{\rm Si}_{{2}}{\rm B}_{12}{\rm Cu}_{{1}}$
retards growth of
$\alpha$
-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
$\alpha$
-Fe is 2.86652
${\rm\AA}$
, 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
$(T_{{C}})$
of the precipitated
$\alpha$
-Fe to decrease by
$\Delta T_{{C}}=31~{\rm K}$
lower than the value of pure bcc Fe. With increase in the volume fraction of the precipitated
$\alpha$
-Fe, the concentration of residual amorphous becomes close to that of the most stable amorphous alloy, i.e.,
${\rm Fe}_{{76}}{\rm Si}_{{9}}{\rm B}_{{10}}{\rm P}_{{5}}$
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.