| 1. |
- Gao, Shang, et al.
(author)
-
Dipolar Spin Ice States with a Fast Monopole Hopping Rate in CdEr2X4 (X = Se, S)
- 2018
-
In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 120:13
-
Journal article (peer-reviewed)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. CdEr2Se4 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 Dy2Ti2O7. In this Letter we use diffuse neutron scattering to show that both CdEr2Se4 and CdEr2S4 support a dipolar spin ice state-the host phase for a Coulomb gas of emergent magnetic monopoles. These Coulomb gases have similar parameters to those in Dy2Ti2O7, i.e., dilute and uncorrelated, and 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 Er3+ 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 CdEr2X4 (X = Se, S) are primarily due to much faster monopole hopping. Our work suggests that CdEr2X4 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.
|
|
| 2. |
- Hartmann, Ola, et al.
(author)
-
Magnetic properties of the multiferroic chromium thio-spinels CdCr2S4 and HgCr2S4
- 2013
-
In: European Physical Journal B. - : Springer Science and Business Media LLC. - 1434-6028 .- 1434-6036. ; 86:4, s. 148-
-
Journal article (peer-reviewed)abstract
- Powder samples of CdCr2S4 and HgCr2S4 were investigated with respect to their magnetic behavior using muon spin rotation/relaxation spectroscopy (mu SR). In CdCr2S4, a second order magnetic transition at 83 +/- 1 K is confirmed. No influence on the mu SR magnetic parameters due to the simultaneous ferroelectric transition was detected. In the limit T -> 0, persistent spin fluctuation exists as a consequence of magnetic frustration. The proposed structural transition around 150 K is barely visible in the mu SR spectra, indicating that the change in local symmetry is subtle. In HgCr2S4, we see in zero field at 27 +/- 2 K a second order transition from the paramagnetic into a long-range ordered (LRO) magnetic state. This LRO state is characterized in the mu SR spectra by a spontaneous spin precession signal. Applications of moderate magnetic fields (up to 450 mT) destroy the precession signal in favor of a rapidly decaying exponential signal. It reflects short-range order (SRO) of strongly correlated dynamic spins. The magnitude of the field required to induce this change is dependent on temperature. The observation of an increase of magnetic spin fluctuations with applied field suggests that spin dynamics play a key role in the field induced changes of the magnetic properties.
|
|
