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

Published version
Peer-reviewed

Type

Article

Change log

Authors

Samarakoon, Anjana M 
Grigera, SA 
Tennant, D Alan 
Kirste, Alexander 

Abstract

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.

Description

Keywords

constrained dynamics, frustrated magnets, glass physics, noise measurements, spin ice

Journal Title

Proc Natl Acad Sci U S A

Conference Name

Journal ISSN

0027-8424
1091-6490

Volume Title

119

Publisher

Proceedings of the National Academy of Sciences
Sponsorship
Engineering and Physical Sciences Research Council (EP/K028960/1)
Engineering and Physical Sciences Research Council (EP/M007065/1)
Engineering and Physical Sciences Research Council (EP/P034616/1)
EPSRC (EP/T028580/1)
Engineering and Physical Sciences Research Council (2275086)