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arXiv · 2102.13656

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

A. Scheie·M. Sanders·Yiming Qiu·T. R. Prisk·R. J. Cava·C. Broholm
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Abstract

We report the low temperature magnetic properties of Nd$^{3+}$ pyrochlore $\rm Nd_2ScNbO_7$. 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 $ΔS = R \ln(2)$, 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 $\rm Nd_2Zr_2O_7$. 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 $\rm Nd_2Zr_2O_7$. 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.

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A. Scheie, M. Sanders, Yiming Qiu, T. R. Prisk, R. J. Cava, C. Broholm. 2021-02-26. Beyond magnons in Nd2ScNbO7: An Ising pyrochlore antiferromagnet with all in all out order and random fields. https://doi.org/10.1103/physrevb.104.134418

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