Determination of New Magnetic Structures in LaFeAs1-xPxO

LaFeAs1-xPxO has recently been proposed to display unusual properties as a function of P doping with two distinct superconducting (SC) domes separated by a possible AFM phase as suggested by NMR spectroscopy. Initial neutron diffraction data obtained over this composition range (0.4 < x < 0.7) failed to reveal the existence of long range magnetic order between the SC domes. The absence of any obvious physical ground state is difficult to understand especially in a range where superconductivity is clearly suppressed without any apparent driving force! Recently, we performed preliminary proof-of-principle measurements using muon spin rotation at EMU and neutron diffraction (long data collection time) on WISH and successfully proved the existence of at least two magnetic phases at different P contents. Careful measurements are needed on WISH, HRPD and EMU as described in the proposal.