  Motivated by recent experiments observing half-integer flux quanta in
mesoscopic loops of superconducting Sr2RuO4, a theory is developed based on a
"d-soliton", a topological defect of spin-triplet superconductors involving a
change of the spin configuration. A phenomenological Ginzburg-Landau free
energy is given which allows to describe such a soliton yielding a half-integer
flux quantum inside a loop, assuming a chiral p-wave superconducting phase. The
d-soliton couples to spin polarization perpendicular to the loop axis, which
allows to reduce the energy of the d-soliton, fitting well to the experimental
findings. The origin of this coupling lies in the combination of spin and
charge current within the d-soliton generating a spin polarization analogous to
a spin Hall effect. The effect of Fermi liquid corrections is discussed, in
particular, in view of the spatial extension of the d-soliton and the
energetics in comparison with a standard integer flux state.
