Neutron diffraction study of magnetic structure and successive 5 electronic transition in the itinerant antiferromagnet NpRhGa

Jonen, Shintaro; Metoki, Naoto   ; Honda, Fuminori; Kaneko, Koji   ; Yamamoto, Etsuji  ; Haga, Yoshinori   ; Aoki, Dai*; Homma, Yoshiya*; Shiokawa, Yoshinobu*; Onuki, Yoshichika*

Neutron diffraction experiments have been carried out in a single crystal of NpRhGa in order to reveal the magnetic structure and 5 electronic state of this compound. An antiferromagnetic structure with the propagation vector = (0 0 1/2) appears below . We found a remarkable change in the moment direction at , namely, the Np moment is parallel to the -axis for (AF1), but parallel to the 110 direction for (AF2). The magnitude of magnetic moment exhibits a discontinuous change at , indicating that the moment reorientation is associated with a change of the 5 electronic state. This transition might be the consequence of the competition between the magnetic and/or quadrupolar interaction in the low-moment and high-moment states. The observed magnetic form factor indicates a dominant contribution from the orbital moment, but the orbital contribution is reduced from the Np free ion state. This is consistent with the itinerant character of the 5 electrons in NpRhGa, which is revealed by dHvA experiments and band structure calculations.