Influence of Thermal Treatment and Crystal Growth on the Final Composition and Magnetic Properties of the YFe_xAl_12-x (4 ≤ x ≤ 4.2) Intermetallics

Abstract

A study by powder X-ray diffraction (using the Rietveld method of structure refinement), 57 Fe Mo ¨ssbauer spectroscopy, and magnetization measurements have shown that YFe 4 Al 8 , 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 YFe 4.2(2) Al 7.8(2) (space group I4/mmm, a ) 8.7303(3) Å, c ) 5.0486(2) Å). YFe 4.2 Al 7.8 shows an antiferromagnetic-like transition at T ord ) 100 K, in contrast with YFe 4 Al 8 (T ord ) 180 K). In YFe 4.2 Al 7.8 a distribution of the moduli of the Fe magnetic moments (µ Fe ) is observed between 100 K and ∼50 K. Below 45 K the Fe atoms on the 8f site have two different values of µ Fe and on the 8j sites only one is observed. The relative values of the µ Fe may be understood on the basis of the Fe-Fe intersite exchange interactions.

Static and dynamic magnetic study of DyFexAl12−x (4≤x≤4.7)

“…2) the Mö ssbauer spectrum taken at room temperature shows an asymmetric doublet in contrast to DyFe 4 Al 8 . Also the 10 K Mö ssbauer spectrum for this composition clearly denotes the presence of Fe atoms on the 8j site: small shoulders are apparent on the outer peaks of the lowtemperature sextet [6,20]. In this case at least three magnetic sextets are needed to obtain a proper fit of the spectrum.…”

“…In the ordered AFe 4 Al 8 compounds the A atoms are located on the 2a sites at the origin and center of the unit cell, the Fe atoms occupy only the 8f positions and the Al the 8i positions. With increasing Fe content the Fe atoms share the 8j positions with Al atoms [3][4][5][6]. These systems present complex magnetic properties, even in the simplest cases such as AFe 4 Al 8 (A ¼ Y, Lu), where the iron atoms are located in only one crystallographic position (8f) and the f-element is non-magnetic [7].…”

“…In order to clarify the magnetism of the RFe x Al 12Àx compounds and within the frame of a systematic study of the A-Fe-Al (A ¼ U, Y) ternary systems undertaken by us in the last years [6,16,17], a detailed study by powder X-ray diffraction (XRD), magnetization, AC-susceptibility and 57 Fe Mö ssbauer spectroscopy of DyFe x Al 12Àx (4 x 4.7) was performed.…”

Crystal structure, 57Fe Mössbauer spectroscopy and magnetization of UxFe6Sn6 (0≤x≤0.6)

“…In the isostructural A x Fe 6 Ge 6 series the U compound also shows the lowest B hf [12,16,24]. Furthermore, in other series of isostructural U-and R-containing compounds, such as A 2 Fe 12 Al 5 [25] and AFe x Al 12Kx [3,4,20], the observed B hf are lower in the U-containing compounds, except in the case of AFe 4 Al 8 where they are similar.…”

“…Among those with potentially useful applications as hard magnets, a large variety of magnetic interactions as well as unusual magnetic behaviours, such as in AFe 4 Al 8 [1][2][3][4][5][6][7], have been reported.…”