Crystal structure and physical properties of trigonal NpGa and NpGa

Haga, Yoshinori   ; Aoki, Dai*; Homma, Yoshiya*; Matsuda, Tatsuma; Ikeda, Shugo*; Sakai, Hironori   ; Yamamoto, Etsuji  ; Nakamura, Akio; Shiokawa, Yoshinobu*; Onuki, Yoshichika

We report reinvestigation the Np-Ga binary system. We successfully obtained NpGa single crystals. Detailed investigation of the crystal structure using the single-crystal X-ray diffraction has shown that the flux-grown NpGa crystallizes not in cubic but in the trigonal Rm structure. It orders ferromagnetically at 70 K with the saturation moment of 1.5 /Np. It is interesting to note that the cubic NpGa orders antimagnetically at similar temperature 62 and become ferromagnetic under magnetic field with the similar saturation moment 1.6 /Np. These characteristics are understood from the structural point of view.