Аннотация:NpP orders at ${T}_{N}\ensuremath{\sim}120\mathrm{K}$ into an incommensurate longitudinal antiferromagnetic structure and becomes commensurate with $\mathbf{k}=〈\frac{1}{3}00〉$ at ${T}_{\mathrm{com}}=70\mathrm{K}$ with a first-order phase transition. We have examined the magnetic phase diagram with resonant x-ray magnetic scattering (RXMS) on a single crystal of NpP with the photon energy tuned to the Np ${M}_{4}$ edge at 3.846 keV. A number of phases are present just above ${T}_{\mathrm{com}}$ but in the lower 3+, 3- phase a single peak is observed, together with a tetragonal distortion. Our study is in agreement with earlier neutron work, but the increased wave vector resolution with RXMS gives more details. A satellite at $2k$ was observed below ${T}_{\mathrm{com}}$ in the unrotated $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\sigma}}\ensuremath{\sigma}$ polarization channel with a strong dependence on the incident photon energy. A model for this is proposed by considering small differences in the charge distribution around the two independent Np sites in the commensurate 3+, 3- phase, and is consistent with the observation by M\"ossbauer spectroscopy of two different electric quadrupole moments in this temperature range. However, to determine the origin of this signal its intensity as a function of the azimuthal angle must be determined.
