Spin Ice: Magnetic Excitations without Monopole Signatures using Muon Spin Rotation

ORAL

Abstract

Theory predicts the low-temperature magnetic excitations in spin ices consist of deconfined magnetic charges, or monopoles. A recent transverse-field (TF) muon spin rotation ($\mu$SR) experiment [S T Bramwell {\it et al}, Nature {\bf 461}, 956 (2009)] reports results claiming to be consistent with the temperature and magnetic field dependence anticipated for monopole nucleation $-$ the so-called second Wien effect. We demonstrate via a new series of $\mu$SR experiments in Dy$_2$Ti$_2$O$_7$ that such an effect is not observable in TF $\mu$SR. Rather, as found in many highly frustrated magnetic materials, we observe spin fluctuations which become temperature independent at low temperatures, behavior which dominates over any possible signature of thermally nucleated monopole excitations.

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Authors

  • Sarah Dunsiger

    • Physik Department, Technische Universitaet Muenchen, D-85748 Garching, Germany

  • Michel Gingras

    • University of Waterloo
    • Department of Physics and Astronomy, University of Waterloo, Waterloo, Ontario, N2L 3G1, Canada

  • Graeme Luke

    • McMaster University
    • Department of Physics and Astronomy, McMaster University, Hamilton, Ontario L8S 4M1, Canada

  • Yasutomo Uemura

    • Department of Physics, Columbia University
    • Department of Physics, Columbia University, New York, New York 10027, USA