High pressure magnetic state of MnP probed by means of muon-spin   rotation
  We report a detailed $\mu$SR 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 ${\bf Q}$ 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 appear to support that the magnetic state from which superconductivity develops at higher pressures is an incommensurate helical phase. 
R. Khasanov, A. Amato, P. Bonf\`a, Z. Guguchia, H. Luetkens, E.   Morenzoni, R. De Renzi, N.D. Zhigadlo
cond-mat.supr-con cond-mat.str-el