Magnets frustrated by competing exhange (TbFe sub 6 Al sub 6 and ErFe sub 6 Al sub 6 )

Frustration in the RFe sub 6 Al sub 6 intermetallics originates from competition between ferromagnetic inter- and antiferromagnetic intra-sublattice exchange in conjunction with crystallographic disorder of the Fe-Al sublattice. The mu SR data give no indication for the presence of a spin-glass-like state below their ferrimagnetic ordering temperature of approx340K. The dominant feature of frustration observed by mu SR is persistent spin fluctuations well below the ordering temperature. The quasi-static limit is only reached around 50K, which coincides with the temperature where local magnetization saturates. Furthermore, there is evidence that the magnetic ordering of the 8j sublattice with its random occupation of Al and Fe ions is retarded.