  The Kondo-lattice model, which couples a lattice of localized magnetic
moments to conduction electrons, is often used to describe heavy-fermion
systems. Because of the interplay between Kondo physics and magnetic order it
displays very complex behavior and is notoriously hard to solve. The
ferromagnetic Kondo-lattice model, with a ferromagnetic coupling between the
local moments, describes a phase transition from a paramagnetic phase to a
ferromagnetic one as a function of either temperature or the ferromagnetic
local-moment coupling. At zero temperature, this is a quantum phase transition
that has received considerable attention. It has been theoretically described
to be continuous, or second order. Here we show that this belief is mistaken;
in the absence of quenched disorder the quantum phase transition is first
order, in agreement with experiments, as is the corresponding transition in
other metallic ferromagnets.
