High-pressure magnetic state of MnP probed by means of muon-spin rotation

We report a detailed muon-spin rotation study of the pressure evolution of the magnetic order in the manganese-based pnictide MnP, which has been recently found to undergo a superconducting transition under pressure once the magnetic ground state is suppressed. Using the muon as a volume sensitive local magnetic probe, we identify a ferromagnetic state as well as two incommensurate helical states (with propagation vectors Q aligned along the crystallographic c and b directions, respectively) which transform into each other through first-order phase transitions as a function of pressure and temperature. Our data suggest that the magnetic state from which superconductivity develops at higher pressures is an incommensurate helical phase.