High Pressure Route to Magnetic Monopole Dimers in Spin Ice

Published

September 20, 2011

Author(s)

H. D. Zhou, S.T. Bramwell, J. G. Cheng, C. R. Wiebe, G. Li, L. Balicas, J. A. Bloxsom, H. J. Silverstein, J. S. Zhou, J. B. Goodenough, Jason S. Gardner

Abstract

The gas of magnetic monopoles in spin ice is governed by one key parameter: the monopole chemical potential^1,2. A significant variation of this parameter could access hitherto undiscovered magnetic phenomena arising from monopole correlations, as observed in the analogous electrical Coulomb gas: for example monopole dimerisation, critical phase separation, or charge ordering^3-5. However, all the known spin ice materials have values of chemical potential imposed by their structure and chemistry that place them deeply within the weakly correlated regime, so none of these interesting phenomena occur. By using extremely high pressures, we have extended the range of stability of the cubic pyrochlore structure that supports spin ice behaviour, and so created a new monopole host with a radically different chemical potential. In particular, we have prepared cubic Dy₂Ge₂O₇ which may be considered a denser version of the canonical spin ice Dy₂Ti₂O₇. We demonstrate that Dy₂Ge₂O₇ is an ideal magnetic Coulomb gas, being almost perfectly described by the classic electrolyte theory of De-bye, Hückel and Bjerrum over an extraordinarily wide range of temperature. The monopole chemical potential of Dy₂Ge₂O₇ is shown to place this material on the boundary between regimes of strong and weak correlation, resulting in significant monopole dimerisation at all temperatures. Our results show that very large variations in chemical potential are possible in real spin ice materials, leading to diverse collective properties of magnetic monopoles.

Citation

Nature Communications

Volume

478

Pub Type

Journals

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Keywords

pyrochlores, monopoles, heat capacity

Citation

Zhou, H. , Bramwell, S. , Cheng, J. , Wiebe, C. , Li, G. , Balicas, L. , Bloxsom, J. , Silverstein, H. , Zhou, J. , Goodenough, J. and Gardner, J. (2011), High Pressure Route to Magnetic Monopole Dimers in Spin Ice, Nature Communications, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=907810 (Accessed July 27, 2024)