  Chiral nematic liquid crystals sometimes form blue phases characterized by
spirals twisting in different directions. By combining model calculations with
neutron-scattering experiments, we show that the magnetic analogue of blue
phases does form in the chiral itinerant magnet MnSi in a large part of the
phase diagram. The properties of this blue phase explain a number of previously
reported puzzling features of MnSi such as partial magnetic order and a
two-component specific-heat and thermal-expansion anomaly at the magnetic
transition.
