Magnetic order and hyperfine interactions in RFe 6Al 6 ( R = rare earth)

Abstract

The systems RFe 6Al 6( R = Y, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb) crystallize in the tetragonal body centered I4/ mmm structure. In striking contrast to the magnetic behaviour of RFe 4Al 8 (weakly coupled R and Fe sublattices, complicated magnetic structure, low T c ~ 130 K), in the RFe 6Al 6 systems all magnetic sublattices order simultaneously at a relatively high temperature. The magnetization curves start with low values at low temperatures and rise to very high values at T max ~ 230 K and then drop to 0 at T c ~ 330 K. All samples show strong hysteresis effects at temperatures just below T max. Mossbauer studies of 57Fe in the ( f) and ( j) sites and 151Eu, 155Gd, 161Dy, 166Er and 170Yb in the ( a) site yield all hyperfine interaction parameters and temperature dependence of the local magnetic moments. All Mossbauer and magnetization experimental results can be explained in a self consistent way with a simple molecular field model. The Fe in the ( j) site plays the dominant role in its strong intrasublattice ferromagnetic exchange and its strong antiferromagnetic exchange with the rare earth site. The Fe in the ( f) site have an antiferromagnetic intrasublattice exchange, they have a canted strcuture with the ferromagnetic component parallel to the ( j) sublattice magnetization.