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 Nd3+ pyrochlore Nd2ScNbO7. Susceptibility and magnetization show an easy-axis moment, and heat capacity reveals a phase transition to long-range order at TN=371(2) mK with a fully recovered ΔS=Rln(2), 53% of it recovered for T>TN. 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 Nd2Zr2O7. Nuclear hyperfine excitations measured by ultra-high-resolution neutron backscattering indicate a distribution of static electronic moments below TN, which may be due to B-site disorder influencing Nd crystal electric fields. Analysis of heat-capacity data shows an unexpected T-linear or T3/2 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 Nd2Zr2O7. 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.