Magnetic ordering in ternary rare earth iron aluminium compounds (RFe4Al8)

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Abstract
The magnetic properties of the tetragonal ternary compounds RFe4Al8(R=La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y and Th) were investigated. An analysis of the data is given in terms of a molecular field model involving three magnetic sublattices: the R sublattice and two antiparallel-coupled Fe sublattices. It was found that in RFe4Al8 the iron moments are coupled antiparallel to the rare earth spin moments. Estimates are given of the molecular field constants associated with the R-Fe interaction and the Fe intrasublattice interaction. Most of these compounds were also investigated by 57Fe Mossbauer spectroscopy. Values are given for the effective hyperfine fields and the isomer shifts. This technique also made possible an accurate determination of the magnetic ordering temperatures, which were difficult to detect by magnetic measurements, even though the Fe moment is about 0.7 mu B/Fe in the magnetically ordered state. The magnetic ordering temperatures range from 140 to 200K. The effective moment of the Fe atom in the paramagnetic regime is about 3.8 mu B/Fe. The magnetic properties of GdMn4Al8 and YMn4Al8 were also determined.