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arXiv · 1705.10737

Dipolar spin ice states with fast monopole hopping rate in CdEr$_2$X$_4$ (X = Se, S)

Shang Gao·Oksana Zaharko·Vladimir Tsurkan·Lilian Prodan·Edward Riordan·Jorge Lago·Björn Fåk·Andrew Wildes·Marek M. Koza·Clemens Ritter·Peter Fouquet·Lukas Keller·Emmanuel Canévet·Marisa Medarde·Jakob Blomgren·Christer Johansson·Sean R. Giblin·Stanislav Vrtnik·Jože Luzar·Alois Loidl·Christian Rüegg·Tom Fennell
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Abstract

Excitations in a spin ice behave as magnetic monopoles, and their population and mobility control the dynamics of a spin ice at low temperature. CdEr$_2$Se$_4$ is reported to have the Pauling entropy characteristic of a spin ice, but its dynamics are three-orders of magnitude faster than the canonical spin ice Dy$_2$Ti$_2$O$_7$. In this letter we use diffuse neutron scattering to show that both CdEr$_2$Se$_4$ and CdEr$_2$S$_4$ support a dipolar spin ice state -- the host phase for a Coulomb gas of emergent magnetic monopoles. These Coulomb gases have similar parameters to that in Dy$_2$Ti$_2$O$_7$, i.e. dilute and uncorrelated, so cannot provide three-orders faster dynamics through a larger monopole population alone. We investigate the monopole dynamics using ac susceptometry and neutron spin echo spectroscopy, and verify the crystal electric field Hamiltonian of the Er$^{3+}$ ions using inelastic neutron scattering. A quantitative calculation of the monopole hopping rate using our Coulomb gas and crystal electric field parameters shows that the fast dynamics in CdEr$_2$X$_4$ (X = Se, S) are primarily due to much faster monopole hopping. Our work suggests that CdEr$_2$X$_4$ offer the possibility to study alternative spin ice ground states and dynamics, with equilibration possible at much lower temperatures than the rare earth pyrochlore examples.

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Shang Gao, Oksana Zaharko, Vladimir Tsurkan, Lilian Prodan, Edward Riordan, Jorge Lago, Björn Fåk, Andrew Wildes, Marek M. Koza, Clemens Ritter, Peter Fouquet, Lukas Keller, Emmanuel Canévet, Marisa Medarde, Jakob Blomgren, Christer Johansson, Sean R. Giblin, Stanislav Vrtnik, Jože Luzar, Alois Loidl, Christian Rüegg, Tom Fennell. 2018-03-20. Dipolar spin ice states with fast monopole hopping rate in CdEr$_2$X$_4$ (X = Se, S). https://doi.org/10.1103/physrevlett.120.137201

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