Resonant x-ray scattering study of NpRhGa_5 and NpCoGa_5

TL;DR

This study uses resonant x-ray scattering to investigate the magnetic structures of NpCoGa_5 and NpRhGa_5, revealing details about magnetic moment orientations, domain populations, and orbital polarization effects at the atomic level.

Contribution

It provides new insights into the magnetic ordering and hybridization effects in neptunium gallide compounds using resonant x-ray scattering at multiple absorption edges.

Findings

Magnetic moments align along [001] in NpCoGa_5.

In NpRhGa_5, moments reorient from c-axis to ab plane.

Ga 4p orbital polarization correlates with Np magnetic moments.

Abstract

We report a resonant x-ray scattering (RXS) study of antiferromagnetic neptunium compounds NpCoGa_5 and NpRhGa_5 at the Np M_4 and Ga K-edges. Large resonant signals of magnetic dipole character are observed below the Neel temperatures at both edges. The signals at the Np edges confirm the behaviour determined previously from neutron diffraction, i.e. the moments along [001] in NpCoGa_{5} and in NpRhGa_5 a reorientation of the moments from the c-axis direction to the ab plane. In the latter material, on application of magnetic field of 9 Tesla along the [010] direction we observe a change in the population of different [110]-type domains. We observe also a magnetic dipole signal at the Ga K-edge, similarly to the reported UGa_3 case, that can be interpreted within a semi-localized model as an orbital polarization of the Ga 4p states induced via strong hybridization with the Np 5f valence band. Quantitative analysis of the signal shows that the Ga dipole on the two different Ga sites follows closely the Np magnetic moment reorientation in NpRhGa_5. The ratios of the signals on the two inequivalent Ga sites are not the same for the different compounds.