  We present a phenomenological theory of spin-orbit torques in a metallic
ferromagnet with spin-relaxing boundaries. The model is rooted in the coupled
diffusion of charge and spin in the bulk of the ferromagnet, where we account
for the anomalous and spin Hall effects, as well as the anisotropic
magnetoresistance, in the corresponding constitutive relations, for both charge
and spin sectors. The diffusion equations are supplemented with suitable
boundary conditions reflecting the spin-sink capacity of the environment. In
inversion-asymmetric heterostructures, the uncompensated spin accumulation
exerts a dissipative torque on the order parameter, giving rise to a
current-dependent linewidth in the ferromagnetic resonance. We compare our
model to recent spin-torque ferromagnetic resonance measurements, illustrating
how rich self-induced spin-torque phenomenology can arise even in simple
magnetic structures.
