Anomalous magnetic noise in an imperfectly flat landscape in the topological magnet Dy_2Ti_2O_7

Noise generated by motion of charge and spin provides a unique window into materials at the atomic scale. From temperature of resistors to electrons breaking into fractional quasiparticles , “listening” to the noise spectrum is a powerful way to decode underlying dynamics. Here, we use ultrasensitive SQUIDS to probe the puzzling noise in a frustrated magnet, the spin-ice compound Dy2Ti2O7 (DTO), revealing cooperative and memory effects. DTO is the first topological magnet in three dimensions–characterised by an emergent magnetostatics and tell-tale fractionalized magnetic monopole quasiparticles–whose real-time dynamical properties have been an enigma from the very beginning. We show that DTO exhibits highly anomalous noise spectra, differing significantly from the expected Brownian noise of monopole random walks, in three qualitatively different regimes: equilibrium spin ice, a ‘frozen’ regime extending to ultra-low temperatures, as well as a high-temperature ‘anomalous’ paramagnet. We present several distinct mechanisms which give rise to varied coloured noise spectra. In addition, we identify the structure of the local spin-flip dynamics as a crucial ingredient for any modelling. Thus, the dynamics of spin ice reflects the interplay of local dynamics with emergent topological degrees of freedom and a frustration-generated imperfectly flat energy landscape, and as such points to intriguing cooperative and memory effects for a broad class of magnetic materials