Influence of thermal treatment and crystal growth on the final compositionand magnetic properties of the YFexAl12-x (4 <= x <= 4.2) Intermetallics

A study by powder X-ray diffraction (using the Rietveld method of structure refinement), Fe-57 Mossbauer spectroscopy, and magnetization measurements have shown that YFe4Al8, although a stable phase at 1070 K (apace group 14/ mmm, a = 8.7604(7) Angstrom, c = 5.0504(5) Angstrom), does not melt congrue ntly. Large single crystals obtained by the Czochralski method from bulk ch arges containing Y, Fe, and Al in the atomic ratios 1/4/8 have final compos itions YFe4.2(2)Al7.8(2) (space group 14/mmm, a = 8.7303(3) Angstrom, c = 5 .0486(2) Angstrom). YFe4.2Al7.8 shows an antiferromagnetic-like transition at T-ord 100 K, in contrast with YFe4Al8 (T-ord = 180 K) In YFe4.2Al7.8 a d istribution of the moduli of the Fe magnetic moments (mu(Fe)) is observed b etween 100 K and similar to 50 K. Below 45 K the Fe atoms on the 8f site ha ve two different values of mu(Fe) and on the 8j sites only one is observed. The relative values of the mu(Fe) may be understood on the basis of the Fe -Fe intersite exchange interactions.