MAGNETIC ORDER IN THE PERIODIC ANDERSON MODEL

We study the ground state of the symmetric, finite-U, periodic Anderson model using a mean-field slave-boson theory of the Kotliar-Ruckenstein type. At half filling (two electrons per site) we find a charge gap at all U > 0 and a transition from the paramagnetic to an antiferromagnetically ordered (AF) state at a critical value of the on-site interaction U for given hybridization V. The AF state is found to be lowest in energy within the manifold of spiral magnetic states. Results for the energy, hybridization matrix element, and local moment compare well with quantum Monte Carlo results for finite systems. Lowering the density induces a smooth crossover from AF to ferromagnetic (F) order via a spiral phase. Closely above 1/4 filling a first order transition from F to AF order is found. The insulating state at 1/4 filling is shown to be described by an AF Heisenberg model.