  Spin-triplet superfluids can support exotic objects, such as half-quantum
vortices characterized by the nontrivial winding of the spin structure. We
present cantilever magnetometry measurements performed on mesoscopic samples of
Sr2RuO4, a spin-triplet superconductor. For micron-sized annular-shaped
samples, we observe transitions between integer fluxoid states, as well as a
regime characterized by "half-integer transitions," i.e., steps in the
magnetization with half the height of the ones we observe between integer
fluxoid states. These half-height steps are consistent with the existence of
half-quantum vortices in superconducting Sr2RuO4.
