Distinct Magnetic Phase Transition at the Surface of an Antiferromagnet
| Autor: | Nikitas I. Gidopoulos, G. M. Watson, Doon Gibbs, Sean Langridge, Martin Long, C. Vettier, Joseph J. Betouras, Frank Pollmann, G. H. Lander |
|---|---|
| Rok vydání: | 2014 |
| Předmět: |
Condensed Matter - Materials Science
Materials science Condensed Matter - Mesoscale and Nanoscale Physics Strongly Correlated Electrons (cond-mat.str-el) Statistical Mechanics (cond-mat.stat-mech) Condensed matter physics Scattering Materials Science (cond-mat.mtrl-sci) FOS: Physical sciences General Physics and Astronomy Thermal fluctuations Classical XY model Condensed Matter - Strongly Correlated Electrons Ferromagnetism Mesoscale and Nanoscale Physics (cond-mat.mes-hall) Antiferromagnetism Anisotropy Structure factor Néel temperature Condensed Matter - Statistical Mechanics |
| Zdroj: | Physical review letters, 2014, Vol.112(16), pp.167201 [Peer Reviewed Journal] |
| ISSN: | 1079-7114 0031-9007 |
| Popis: | In the majority of magnetic systems the surface is required to order at the same temperature as the bulk. In the present study, we report a distinct and unexpected surface magnetic phase transition, uniquely at a lower temperature than the N\'eel temperature. Employing grazing incidence X-ray resonant magnetic scattering we have observed the near surface behavior of uranium dioxide. UO$_2$ is a non-collinear, triple-q, antiferromagnet with the U ions on an face-centered-cubic lattice. Theoretical investigations establish that at the surface the energy increase, due to the lost bonds, reduces when the spins near the surface rotate, gradually losing their normal to the surface component. At the surface the lowest-energy spin configuration has a double-q (planar) structure. With increasing temperature, thermal fluctuations saturate the in-plane crystal field anisotropy at the surface, leading to soft excitations that have ferromagnetic $XY$ character and are decoupled from the bulk. The structure factor of a finite two-dimensional $XY$ model, fits the experimental data well for several orders of magnitude of the scattered intensity. Our results support a distinct magnetic transition at the surface in the Kosterlitz-Thouless universality class. Comment: 7 pages including Supplemental material, 4 figures |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|