Speaker
Prof.
Patrik Henelius
(Theoretical Physics, KTH)
Description
Spin ices, frustrated magnetic materials analogous to common water ice, have emerged over the past fifteen years as exemplars of high frustration in three dimensions. By analyzing existing experimental data and carefully remeasuring the thermodynamic quantity $\chi T$ we find that in this material, small effective spin-spin exchange interactions compete with the magnetostatic dipolar interaction responsible for the main spin ice phenomenology. This causes an unexpected ``refrustration'' of the long-range order that would be expected from the incompletely self-screened dipolar interaction and which positions the material at the boundary between two competing classical long-range ordered ground states, very close to where theory suggests that a continuous transition described by a noncompact CP$^1$ theory. Furthermore, experimentally we find an interaction-induced peak in $\chi T$, and identify it with a magnetic Joule temperature, where $\partial U\partial M=0$, and the onset of antiferromagnetic correlations. In addition, we find a magnetic Boyle temperature, where $\chi T/C=1$, and the the ferromagnet turns to an antiferromagnet. We provide a phenomenological model to show how the effects of weak frustrated exchange interactions are elevated to high temperature.
Primary author
Prof.
Patrik Henelius
(Theoretical Physics, KTH)
Co-authors
Dr
Laura Bovo
(University College London)
Prof.
Michel Gingras
(University of Waterloo)
Mr
Mikael Twengström
(KTH)
Prof.
Steven Bramwell
(University College London)
