57Fe Moessbauer spectroscopy and magnetization study of YFexAl12-x (4.4≤x≤5)

YFexAl12-x in the composition range 4.4≤x≤5 was prepared by induction melting followed by annealing in vacuum at 1270 K. Magnetization data below 150 K show complex magnetic behaviour dependent on applied field, composition and temperature. The transition temperature Tc, corresponding to the main maximum of the magnetization vs. temperature curves and below which magnetic interactions are observed for a significant fraction of the Fe atoms in the Moessbauer spectra, decreases from 180 K for x=4 down to 100 K for 4.2≤x≤4.7 and rises again up to 160 K for x=5. The analysis of the spectra obtained at 5 K is consistent with full occupation of the 8f sites by Fe atoms and sharing of the 8j sites by Fe and Al as deduced from the Rietveld analysis of X-ray powder diffraction data. The Moessbauer spectra further show a dependence of magnetic hyperfine fields and isomer shifts on the crystallographic site and on the number of the Fe nearest neighbours similar to that observed in UFexAl12-x (4≤x≤6) and RFexAl12-x (R=Y, Lu, x=4, 4.2). The magnetic properties of the UFexAl12-x and YFexAl12-x series are compared and the magnetic interactions between the different Fe sublattices are discussed