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High Pressure Route to Magnetic Monopole Dimers in Spin Ice



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


The gas of magnetic monopoles in spin ice is governed by one key parameter: the monopole chemical potential1,2. 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 ordering3-5. 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.
Nature Communications


pyrochlores, monopoles, heat capacity


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], (Accessed April 16, 2024)
Created September 19, 2011, Updated October 12, 2021