Disorder Dependence of the Ferromagnetic Quantum Phase Transition

We quantitatively discuss the influence of quenched disorder on the ferromagnetic quantum phase transition in metals, using a theory that describes the coupling of the magnetization to gapless fermionic excitations. In clean systems, the transition is first order below a tricritical temperature T-tc. Quenched disorder is predicted to suppress T-tc until it vanishes for residual resistivities rho(0) on the order of several mu Omega cm for typical quantum ferromagnets. We discuss experiments that allow us to distinguish the mechanism considered from other possible realizations of a first-order transition.