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

Abstract

We report the low-temperature magnetic properties of Nd3+ pyrochlore Nd2⁢ScNbO7. 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 Δ⁢𝑆=𝑅⁢ln⁡(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 Nd2⁢Zr2⁢O7. 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 Nd2⁢Zr2⁢O7. 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.