We report the results of a study carried out on a neptunium-transition-metal binary compound Np₂Ni₁₇ that has been synthesized and characterized by means of Powder X-Ray Diffraction, Superconducting-Quantum-Interference-Device magnetometry (SQUID), ²³⁷Np Mössbauer spectroscopy (Fig. 1) and specific heat. Np₂Ni₁₇ is daughter compound of the recently reported[1] NpNi₅ and is an analogue of the previously reported[2] Np₂Co₁₇, (both are Ferromagnetic compounds) like its analogue Np₂Ni₁₇ crystallized in the Th₂Ni₁₇ hexagonal structure (P6₃/mmc space group no. 194) with a room temperature lattice parameters a = 8.28215(7)Å and c = 8.04029(8)Å contain two non-equivalent Np sites. However unlike its analogue (and parent) Np₂Ni₁₇ exhibits an antiferromagnetic order below T_N ~ 17.5 K with a complex low temperature magnetization curves. Mössbauer spectra below T_N show two ordered Np sites, one with a huge ordered moment (μ_Np ~ 2.25 μ_B) and the other carry hardly any ordered moment at all (μ_Np ~ 0.2 μ_B). Specific heat measurements (C_P) confirmed the onset of an antiferromagnetic order below T_N as well as showing a complex low temperature curve with what might be a second phase transition below ~ 1 K.

[1] A. Hen et al PHYSICAL REVIEW B 90, 054408 (2014).

[2] I. Halevy et al PHYSICAL REVIEW B 85, 014434 (2012)