Influence of Thermal Treatment and Crystal Growth on the Final Composition and Magnetic Properties of the YFe<i>_x</i>Al_12-<i>_x</i> (4 ≤ <i>x</i> ≤ 4.2) Intermetallics

Abstract

A study by powder X-ray diffraction (using the Rietveld method of structure refinement), 57Fe Mössbauer spectroscopy, and magnetization measurements have shown that YFe4Al8, although a stable phase at 1070 K (space group I4/mmm, a = 8.7604(7) Å, c = 5.0504(5) Å), does not melt congruently. Large single crystals obtained by the Czochralski method from bulk charges containing Y, Fe, and Al in the atomic ratios 1/4/8 have final compositions YFe4.2(2)Al7.8(2) (space group I4/mmm, a = 8.7303(3) Å, c = 5.0486(2) Å). YFe4.2Al7.8 shows an antiferromagnetic-like transition at Tord = 100 K, in contrast with YFe4Al8 (Tord = 180 K). In YFe4.2Al7.8 a distribution of the moduli of the Fe magnetic moments (μFe) is observed between 100 K and ∼50 K. Below 45 K the Fe atoms on the 8f site have two different values of μFe and on the 8j sites only one is observed. The relative values of the μFe may be understood on the basis of the Fe−Fe intersite exchange interactions.