Crystallization process and magnetic properties of Fe_100−x ,B _x (10 ≦ × ≦ 35) amorphous alloys and supersaturated state of boron inα-Fe

Abstract

Amorphous specimens of Fe_100−x B _x were prepared in the range 10 ≦× ≦ 35 at % B by a single-roller method. The crystallization process and the boron concentration dependence of the Curie temperature were examined by differential scanning calorimetry, X-ray diffraction, Mössbauer spectroscopy and magnetic measurements. Two-step crystallization was observed in specimens with× < 17: amorphous → amorphous + boron-supersaturated b c c phase (α-Fe(B)) → t-Fe₃B +α-Fe. A singleα-Fe(B) phase was not observed. The transition temperature from t-Fe₃B to stable (α-Fe + t-Fe₂B) sensitively depends on the boron content in the alloys. The crystallization temperature (T _x) of the amorphous alloys was almost unchanged for 17 ≦× ≦ 31, but increased remarkably at high boron concentrations of× ≧ 33, where the decomposition products consisted of t-Fe₂B and o-FeB. The Curie temperature (T _c) of the amorphous phase was as low as 480 K at× = 10, increased with increasing boron content up to 820 K and then decreased in the high boron concentration alloys of× > 28. A singleα-Fe(B) phase was not detected in the as-quenched specimens of× = 8 and 10. The phase coexisted with the o-Fe₃B and amorphous phases. The lattice parameter of the phase was 0.2861₀ nm which was smaller than that of pure iron by 2/1000, indicating the substitutional occupation of boron atoms in the b c c lattice.