Abstract
The wave vector q of the magnetic order observed in the heavy rare earth metals is calculated on a model using an exchange interaction between the localized moments and the conduction electrons, assumed free. For a finite amount of order, energy gaps appear in the conduction bands at new Brillouin `superzone' boundaries associated with q. The Fermi surface is distorted by these boundaries. The total energy of the system is computed for finite order and minimized with respect to q. For small order this leads to the usual Ruderman-Kittel result, but as the order increases the value of q at the minimum decreases. The agreement with experiment is good for the simple model of Tm, Er and Ho, but less satisfactory in Dy and Tb where spin-disorder scattering is important. A modification of this model also accounts for the behaviour of the electrical resistivity. It indicates that the real Fermi surface lies just inside the plane hexagonal faces of the Brillouin zone, and that a large area of it is destroyed by the magnetic ordering.