Itinerant helimagnet MnSi

Manganese silicide (MnSi), a model helimagnetic compound, crystallizes in a B20 structure, whose non-centro-symmetric space group $P2_13$ allows a helical (chiral) magnetic structure. The magnetic phase transition temperature of MnSi (29 K at atmospheric pressure) decreases with pressure and approaches zero at about 1.4 GPa. This fact, pointing to possible quantum critical phenomena, has prompted high-pressure studies of MnSi that have revealed a number of fascinating phenomena, in particular, the non-Fermi-liquid behavior of electrical resistivity and the unusual spin state (partial ordering) in the paramagnetic phase. We discuss experimental results characterizing the physical properties and the phase diagram of MnSi and at the same time forming the basis of current ideas in the physics of strongly correlated chiral electron systems.