Beyond magnons in Nd2ScNbO7: An Ising pyrochlore antiferromagnet with all in all out order and random fields

We report the low temperature magnetic properties of Nd 3+ pyrochlore Nd 2 ScNbO 7 . Susceptibility and magnetization show an easy-axis moment, and heat capacity reveals a phase transition to long range order at T N = 371(2) mK with a fully recovered ∆ S = R ln(2) , 53% of it recovered for T > T N . Elastic neutron scattering shows a long-range all-in-all-out magnetic order with low- Q diffuse elastic scattering. Inelastic neutron scattering shows a low-energy flat-band, indicating a magnetic Hamiltonian similar to Nd 2 Zr 2 O 7 . Nuclear hyperfine excitations measured by ultra-high-resolution neutron backscattering indicates a distribution of static electronic moments below T N , which may be due to B-site disorder influencing Nd crystal electric fields. Analysis of heat capacity data shows an unexpected T -linear or T 3 / 2 term which is inconsistent with conventional magnon quasiparticles, but is consistent with fractionalized spinons or gapless local spin excitations. We use legacy data to show similar behavior in Nd 2 Zr 2 O 7 . Comparing local static moments also reveals a suppression of the nuclear Schottky anomaly in temperature, evidencing a fraction of Nd sites with nearly zero static moment, consistent with exchange-disorder-induced random singlet formation. Taken together, these measurements suggest an unusual fluctuating magnetic ground state which mimics a spin-liquid—but may not actually be one.