Speaker
Description
Pyrochlore antiferromagnets (AFM) Gd$_2$$T_2$O$_7$ ($T$: tetravalent metal elements) are prototypical materials for realizing classical spin liquid states. However, most of them have been observed to show long-range magnetic order. Previous studies show that Gd$_2$Hf$_2$O$_7$ has Curie-Weiss temperature $\approx-7.3$ K and a tiny sharp peak on the top of a large broad maximum in the specific heat data indicating a long-range AFM order. Here we present our investigation on the nuclear and magnetic structures of Gd$_2$Hf$_2$O$_7$. Using neutron diffraction, we found that the sample has $\sim8\%$ oxygen Frankel defects with undetectable Gd/Hf antisite defects. The polarized neutron diffuse scattering pattern shows liquid-like scattering at 30 mK without any magnetic Bragg peaks, evidencing a spin-liquid-like ground state. The pattern was further analyzed using reverse Monte Carlo method together with unsupervised machine learning techniques, which reveals a Palmer-Chalker order over the range of a single unit cell. Bond disorder due to oxygen anion disorder may be responsible for the absence of long-range order.
