Magnetic ordering of the heavy rare earths

The magnetic ordering of the rare earths Gd-Tm is studied by means of noncollinear local spin density functional calculations. Er and Tm are found to have helical spin density wave ground states while Gd-Ho are ferromagnetic. The ordering of the border case Ho is shown to be very sensitive to the conduction electron polarization, due to a competition between the Fermi nesting and the exchange splitting, which leads to a conical helix. Although these results are by and large in agreement with experiments the analysis of the obtained results puts some doubt on established hypotheses built into the standard model of rare-earth magnetism.