arXiv subjects

Sean Langridge

Publications and source records attributed to Sean Langridge.

22 records · Page 2Linked to original sources

arXiv2014

Distinct magnetic phase transition at the surface of an antiferromagnet

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 Néel 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.

cond-mat.str-el↗

arXiv2013

Giant topological Hall effect in strained Fe$_{0.7}$Co$_{0.3}$Si epilayers

The coupling of electron spin to real-space magnetic textures leads to a variety of interesting magnetotransport effects. The skyrmionic spin textures often found in chiral B20-lattice magnets give rise, via real-space Berry phases, to the topological Hall effect, but it is typically rather small. Here, B20-ordered Fe$_{0.7}$Co$_{0.3}$Si epilayers display a giant topological Hall effect due to the combination of three favourable properties: they have a high spin-polarisation, a large ordinary Hall coefficient, and dense chiral spin textures. The topological Hall resistivity is as large as 820 n$Ω$cm at helium temperatures. Moreover, we observed a drop in the longitudinal resistivity of 100 n$Ω$cm at low temperatures in the same field range, suggesting that it is also of topological origin. That such strong effects can be found in material grown in thin film form on commercial silicon wafer bodes well for skyrmion-based spintronics.

cond-mat.mes-hall↗

arXiv2013

Spatially homogeneous ferromagnetism below the enhanced Curie temperature in EuO_{1-x} thin films

We have used low energy implanted muons as a volume sensitive probe of the magnetic properties of EuO_{1-x} thin films. We find that static and homogeneous magnetic order persists up to the elevated T_C in the doped samples and the muon signal displays the double dome feature also observed in the sample magnetization. Our results appear incompatible with either the magnetic phase separation or bound magnetic polaron descriptions previously suggested to explain the elevated T_C, but are compatible with an RKKY-like interaction mediating magnetic interactions above 69 K.

cond-mat.str-el↗

arXiv1999

Magnetic Roughness and Domain Correlations in Antiferromagnetically Coupled Multilayers

The in-plane correlation lengths and magnetic disorder of magnetic domains in a transition metal multilayer have been studied using neutron scattering techniques. A new theoretical framework is presented connecting the observed scattering to the in-plane correlation length and the dispersion of the local magnetization vector about the mean macroscopic direction. The results unambiguously show the highly correlated nature of the antiferromagnetically coupled domain structure vertically throughout the multilayer. We are easily able to relate the neutron determined magnetic dispersion and domain correlations to magnetization and magnetotransport experiments.

cond-mat.mtrl-sci↗