Long-range magnetic order of La₂Ni₇

La₂Ni₇ has been recently shown to possess magnetic states associated with low-moment, itinerant Ni ordering.[1] Employing single-crystal neutron diffraction in zero magnetic field, we found one commensurate (C_c) and two incommensurate (IC_ab and IC_c) antiferromagnetic phases below 42.8(5), 58(1), and 62(1) K, respectively. The transition temperatures are consistent with the H-T phase diagrams shown in Ref. [1]. Although IC_ab and IC_c both have the same temperature dependent propagation vector, IC_c has magnetic moments aligned colinear to c whereas IC_ab has a significant magnetic moment component in the ab-plane. We found the phase transition to C_c to be first-order with a magnetic structure consistent with a triangular-wave modulated spin-density wave with magnetic moments colinear along c and propagation vector (0 0 1).

[1] Ribeiro, Raquel A., et al. arXiv:2110.06349 (2021).