We present a circuit model to describe the electron transport through adomain wall in a ferromagnetic nanowire. The domain wall is treated as acoherent 4-terminal device with incoming and outgoing channels of spin up anddown and the spin-dependent scattering in the vicinity of the wall is modelledusing classical resistances. We derive the conductance of the circuit in termsof general conductance parameters for a domain wall. We then calculate theseconductance parameters for the case of ballistic transport through the domainwall, and obtain a simple formula for the domain wall magnetoresistance whichgives a result consistent with recent experiments. The spin transfer torqueexerted on a domain wall by a spin-polarized current is calculated using thecircuit model and an estimate of the speed of the resulting wall motion ismade.
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