Creation and measurement of long-lived magnetic monopole currents in spin ice

Abstract

The recent discovery of ‘magnetricity’ in spin ice raises the question of whether long-lived currents of magnetic ‘monopoles’ can be created and manipulated by applying magnetic fields. Here we show that they can. By applying a magnetic-field pulse to a Dy2Ti2O7 spin-ice crystal at 0.36 K, we create a relaxing magnetic current that lasts for several minutes. We measure the current by means of the electromotive force it induces in a solenoid coupled to a sensitive amplifier, and quantitatively describe it using a chemical kinetic model of point-like charges obeying the Onsager–Wien mechanism of carrier dissociation and recombination. We thus derive the microscopic parameters of monopole motion in spin ice and identify the distinct roles of free and bound magnetic charges. Our results illustrate a basic capacitor effect for magnetic charge and should pave the way for the design and realization of ‘magnetronic’ circuitry.

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Figure 1: Distance dependence of magnetic monopole interactions in spin ice.
Figure 2: An effective capacitor discharge for magnetic monopoles in spin ice.
Figure 3: Demonstration of the requirement for the chemical kinetic model at T=360 mK and its breakdown at higher temperature.
Figure 4: A near-perfect symmetry between electricity and magnetism illustrated by data collapse onto Onsager’s universal curve for the Wien effect16.

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Acknowledgements

It is a pleasure to thank J. Dobson for technical assistance and the following for useful discussions: C. Castelnovo and R. Moessner (in particular for a correspondence concerning the Bjerrum volume), G. Aeppli, B. Kaas, T. Fennell, L. Jaubert and V. Kaiser. P.C.W.H. thanks the Max Planck Institute for Complex Systems, Dresden, for financial support.

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The experimental work was carried out by S.R.G. and I.T., using a sample prepared by D.P. The analysis was carried out by S.T.B. and S.R.G. The theory was devised by S.T.B. and P.C.W.H. The manuscript was written by S.T.B., S.R.G. and P.C.W.H. with input and discussion from all authors.

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Correspondence to S. R. Giblin or S. T. Bramwell.

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The authors declare no competing financial interests.

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Giblin, S., Bramwell, S., Holdsworth, P. et al. Creation and measurement of long-lived magnetic monopole currents in spin ice. Nature Phys 7, 252–258 (2011). https://doi.org/10.1038/nphys1896

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