We report the low-temperature magnetic properties of ${\mathrm{Nd}}^{3+}$ pyrochlore ${\mathrm{Nd}}_2{\mathrm{ScNbO}}_7$. Susceptibility and magnetization show an easy-axis moment, and heat capacity reveals a phase transition to long-range order at $T_N=371\left(2\right)$ mK with a fully recovered $\mathrm{\Delta }S=Rln\left(2\right)$, 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 ${\mathrm{Nd}}_2{\mathrm{Zr}}_2{\mathrm{O}}_7$. Nuclear hyperfine excitations measured by ultra-high-resolution neutron backscattering indicate 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 ${\mathrm{Nd}}_2{\mathrm{Zr}}_2{\mathrm{O}}_7$. 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.

• Received 26 February 2021
• Revised 11 August 2021
• Accepted 4 October 2021

DOI:https://doi.org/10.1103/PhysRevB.104.134418