Origin of anomalous magnetic noise from monopoles in Dy2Ti2O7
In plain words
Magnetization noise in spin ice, produced by moving monopoles, does not follow a simple random-walk picture. Its spectrum and slow relaxation point to constrained monopole motion, but a full quantitative account is lacking.
Precise statement
In Dy2Ti2O7 at $T$ of about 0.5 to 3 K the magnetization-noise spectrum follows $S(\omega) \sim \omega^{-b}$ with $b$ between 1 and 2, and relaxation is faster than Arrhenius would allow at high $T$ and slower at low $T$. Derive $b(T)$ and the relaxation time $\tau(T)$ from a microscopic dipolar model with monopole hopping, without free parameters beyond the fitted exchange set. An answer is a model reproducing $S(\omega, T)$ quantitatively.
What would settle it
Simulations of the fitted dipolar model with realistic monopole hopping that reproduce measured SQUID noise spectra across temperature.
Status in the literature
Dusad et al. (Nature 2019) measured the anomalous noise; Hallen et al. (Science 2022) attributed it to monopole motion on an emergent fractal of accessible sites.