Anomalous magnetic noise in an imperfectly flat landscape in the topological magnet Dy₂Ti₂O₇

Journal Article · 25 January 2022 · Proceedings of the National Academy of Sciences of the United States of America

DOI: https://doi.org/10.1073/pnas.2117453119 · OSTI ID:2469833

Samarakoon, Anjana M. ^[1]; Grigera, S. A. ^[2]; Tennant, D. Alan ^[1]; Kirste, Alexander ^[3]; Klemke, Bastian  ^[4]; Strehlow, Peter ^[3]; Meissner, Michael ^[4]; Hallén, Jonathan N.  ^[5]; Jaubert, Ludovic ^[6]; Castelnovo, Claudio  ^[7]; Moessner, Roderich ^[8]

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1. Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
2. National University of La Plata (Argentina)
3. Physikalisch-Technische Bundesanstalt, Berlin (Germany)
4. Helmholtz-Zentrum Berlin für Materialien und Energie (Germany)
5. Univ. of Cambridge (United Kingdom). Cavendish Lab.; Max Planck Institute for the Physics of Complex Systems, Dresden (Germany)
6. Univ. of Bordeaux (France); Centre National de la Recherche Scientifique (CNRS) (France)
7. Univ. of Cambridge (United Kingdom). Cavendish Lab.
8. Max Planck Institute for the Physics of Complex Systems, Dresden (Germany)

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 superconducting quantum interference device (SQUIDs) to probe the puzzling noise in a frustrated magnet, the spin-ice compound Dy₂Ti₂O₇ (DTO), revealing cooperative and memory effects. DTO is a topological magnet in three dimensions—characterized by emergent magnetostatics and telltale 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 ultralow temperatures, and a high-temperature “anomalous” paramagnet. We present several distinct mechanisms that give rise to varied colored noise spectra. In addition, we identify the structure of the local spin-flip dynamics as a crucial ingredient for any modeling. 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, it points to intriguing cooperative and memory effects for a broad class of magnetic materials.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Oak Ridge Leadership Computing Facility (OLCF)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities (SUF)
• Grant/Contract Number: AC05-00OR22725
• OSTI ID: 2469833
• Journal Information: Proceedings of the National Academy of Sciences of the United States of America, Journal Name: Proceedings of the National Academy of Sciences of the United States of America Journal Issue: 5 Vol. 119; ISSN 0027-8424
• Publisher: National Academy of SciencesCopyright Statement
• Country of Publication: United States
• Language: English