Melt-spun yttrium-iron alloys: Magnetic properties and crystallization kinetics

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Abstract
Magnetic and crystallization data are presented for a series of X‐ray amorphous Y1−xFex (0.4≤x≤0.79) alloys prepared by melt‐spinning. Magnetization measurements, made from 4.2 to 600 K in fields up to 100 kOe, are interpreted on the basis of asperomagnetic structures in which the Fe moment directions are distributed over a decreasing portion of the unit sphere with increasing Fe concentration. In general, the ratio of spontaneous to saturation magnetization, and ordering temperatures, are higher than found for sputtered Y‐Fe alloys, which may indicate a higher degree of compositional short‐range order in these melt‐spun alloys. The thermal stability of the alloys was investigated by differential scanning calorimetry and X‐ray diffraction. Crystallization temperatures varied from 640 K at x=0.4 to 945 K at x=0.79. For the Y‐rich (0.4≤x≤0.5) alloys, crystallization occurs by a multiple stage process, which includes the formation of a metastable Y‐Fe intermetallic phase. Apparent activation energies for the transformations averaged 2.4–3.6 eV, in the range of moderate to high stability glasses. The kinetics of the x=0.67 and 0.75 compositions fit the Johnson‐Mehl‐Avrami relationship with a time dependence of t3–4 up to 65% conversion and t1.7–2.3 thereafter, indicative of a two‐step crystallization mechanism. The coercive force of these melt‐spun alloys was low (200–400 Oe) at all temperatures and, moreover, remained so during crystallization.