ArXiv · 2026
Bond disorder in frustrated pyrochlore antiferromagnets can give rise to fundamentally different quantum ground states depending on the nature of the local magnetic moments. Here, we show that the bond-disordered J_(rm eff)=1/2 pyrochlore antiferromagnet NaCdCo₂F₇ realizes an unconventional spin-glass-like state with continued dynamics, in stark contrast to its isostructural S=1/2 NaCdCu₂F₇ counterpart. High-field magnetization and Co L_(2,3)-edge XAS/XMCD establish spin-orbit-entangled J_(rm eff)=1/2 Co²⁺ moments with a substantial unquenched orbital contribution, consistent with local XY anisotropy seen in the isostructural NaA''Co₂F₇ (A'' = Ca, Sr) analogues. μSR and ²³Na NMR measurements reveal progressive slowing of spin fluctuations below ∼10 K, culminating in a partially frozen state with persistent low-temperature dynamics that deviates from a canonical spin glass. Comparison with the isostructural bond-disordered pyrochlore NaCdCu₂F₇, which realizes a random-singlet state, reveals a fundamentally different response of spin-orbit-entangled Co²⁺ moments to bond disorder. These results identify spin-orbit coupling as a key ingredient governing the fate of bond-disordered frustrated pyrochlore magnets.
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