We investigate the magnetic ground state of CuNdO2, which is a delafossite with a triangular lattice of magnetic Nd3+ ions that are well separated by non-magnetic Cu spacer layers. From inelastic neutron scattering measurements of the crystal electric field, we determine the strong Ising character of the pseudo-spin 1/2 Nd3+ moments. Magnetic susceptibility and heat capacity measurements reveal the onset of long-range antiferromagnetic order at TN=0.78 K. While the magnetic transition is definitively observed with muon spin relaxation, accompanied by the formation of a weakly dispersing spin wave excitation, no dipole-ordered moment is detected with neutron diffraction. We show that the apparent absence of a dipolar ordered moment is a consequence of the dominant Ising character of the antiferromagnetically coupled Nd3+ moments, which experience extreme frustration on the triangular lattice. Consequently, the frustration in CuNdO2 is relieved through in-plane ordering of the substantially smaller perpendicular component of the Nd3+ moments into a 120\textdegree\ structure, with a nearly vanishing ordered moment.
@article{arxiv.2509.23523,
title = {Vanishing ordered moment in the frustrated triangular lattice antiferromagnet CuNdO$_2$},
author = {Jonathan Gaudet and Dalmau Reig-i-Plessis and Bogeng Wen and Thomas J. Hicken and Jonas A. Krieger and Jan Peter Embs and Hubertus Luetkens and Adam A. Aczel and Stuart A. Calder and Matthew B. Stone and Hae-Young Kee and Alannah M. Hallas},
journal= {arXiv preprint arXiv:2509.23523},
year = {2026}
}