Formation, crystal structure and magnetic properties of (1:12) compounds in the Fe–Gd–Mo–Zr system

Abstract

Phase formation in the alloy series Gd8−xZrxFe82Mo10 (x=0–5), Gd8−xZrxFe72Mo20 (x=0–5.5), and Gd8Fe62Mo30−xZrx (x=0–25) has been studied by electron probe X-ray microanalysis and X-ray diffraction followed by Rietveld refinement. For the first two series, the major phase was found to be the (1:12) compound, where Zr partially substitutes for Gd in the 2a crystallographic site of the tetragonal ThMn12-type structure. Simultaneously, a small fraction of Zr atoms enters into the Fe(Mo) sublattice. Up to 1% of Fe(Mo) positions and 46% of Gd-sites can be occupied by Zr-atoms. At high Zr-content, precipitates of elemental Fe and the C14 Laves phase Fe2(Mo,Zr) are formed. The magnetization of the alloys Gd8−xZrxFe82Mo10 has been measured as a function of temperature and magnetic field. Their Curie temperature decreases and the saturation magnetization increases from x=0 to x=2. The coercive force is very small (μ0HC<0.01 T) and independent of composition. In the alloy series Gd8Fe62Mo30−xZrx the (1:12) phase exists only at relatively high Mo-content (x≤10). Zr can substitute for a maximal 7% into Mo positions. Above this limit, the substitution of Gd takes place. For x≥15 the stable phases become the C15 and C36 Laves phases as well as elemental Mo or Gd.