Skyrmion strings and the anomalous Hall effect in CrO2

Area of Science:

• Condensed Matter Physics
• Materials Science
• Statistical Mechanics

Background:

• Topological defects, or singularity points, are hypothesized to be critical in phase transitions of 3D spin systems, analogous to their role in 2D systems like the XY model.
• In double-exchange ferromagnets, conduction electrons interact strongly with core spins via Hund's rule, leading to a Berry phase contribution to the anomalous Hall effect when a nontrivial spin texture is present.

Purpose of the Study:

• To experimentally investigate the role of topological defects in the phase transitions of 3D spin systems.
• To confirm the topological character of critical fluctuations in ferromagnets.
• To establish a link between the behavior of topological spin defect density and thermodynamic properties like heat capacity.

Main Methods:

• Combined Hall effect measurements and magnetization data analysis on Chromium Dioxide (CrO2).
• Applied a thermodynamical scaling hypothesis to analyze the critical behavior.
• Correlated the critical behavior of topological-spin-defect density with the heat capacity.

Main Results:

• The critical behavior of the topological-spin-defect density was found to be consistent with that of the heat capacity.
• This provides the first experimental confirmation of the topological nature of critical fluctuations in such systems.

Conclusions:

• Topological defects play a significant role in the phase transitions of 3D spin systems.
• The study experimentally validates the topological nature of critical fluctuations, supported by the correlation between defect density and heat capacity.
• Findings advance the understanding of critical phenomena in magnetic materials and topological physics.