Suppression of Magnetic Order before the Superconducting Dome in MnP

We have performed neutron diffraction experiments on the manganese superconductor, MnP, under applied pressure. Higher harmonics of the previously reported double helix (2 delta and 3 delta) at ambient pressure were observed and a new magnetic phases was discovered as hydrostatic pressure was applied to a polycrystalline sample below the pressure required to induce superconductivity. The double helix magnetic structure is suppressed by 0.7 GPa. A new incommensurate magnetic structure with propagation vector similar to(0.25, 0.25, 0.125) was found at 1.5 GPa. The application of higher pressures results in the quenching of the incommensurate phase and broad, diffuse magnetic scattering develops before the superconducting phase. Single crystal studies complement the polycrystalline data confirming the magnetic propagation vector in the low pressure phase.