Magnetic phase diagram and change in 5f electronic states in NpNiGa5

Abstract Our neutron scattering study revealed that NpNiGa 5 has a canted structure with the antiferromagnetic (AFM) component along [1 1 0] with q = ( 1 2 1 2 1 2 ) below 18 K, superposed on a ferromagnetic (FM) component along the c -axis. A simple FM order remains stable with elevating temperature ( 18 K T 30 K ) or applying field ( μ 0 H > 8 T ) along [1 1 0]. The large difference in the magnetic moment for these two structures indicates that the transition at T N = 18 K is attributed to the 5f electronic transition between the low-moment FM state and high-moment state accompanying the in-plane AFM component perpendicular to the quantization c -axis. It can be qualitatively understood by a localized 5f model with competing interactions, while the 5f electrons are believed to be itinerant from the partial quenching of the orbital contribution in the magnetic form factor.