Local atomic structure in amorphous Fe-P alloys

Amorphous alloys Fe_x P_100-x have been fabricated by rf sputtering in the composition range 50≤x≤75. Only a-Fe₇₅ P₂₅ is ferromagnetic at 293 K, with its Mössbauer spectrum consisting of six broad lines. This simple spectrum differs markedly from that of c-Fe₃ P. Similarly, thermogravimetric analysis yielded T _c=550 K for the amorphous phase, a value considerably lower than that of the crystalline phase (700 K). The Mössbauer spectra of the samples having x≤71 were all similar quadrupole-split doublets. Mean isomer shifts (IS) and P(H) and P(Q) distributions were determined using Window's method. The isomer shift is nearly independent of concentration in the range studied here, but differs significantly from those of the crystalline compounds c-FeP, c-Fe₂ P, and c-Fe₃ P. The effective quadrupole interaction is also nearly constant for 50≤x≤71, indicating a similar local Fe environment. These results contrast sharply with c-Fe₂ P and c-FeP, which have different crystal symmetries and whose quadrupole interactions differ substantially both from each other and from their amorphous counterparts.