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Magnetic Fluctuations, Precursor Phenomena, and Phase Transition in MnSi under a Magnetic Field
C Pappas1, L J Bannenberg1, E Lelièvre-Berna2
1Delft University of Technology, Mekelweg 15, 2629 JB Delft, Netherlands.
Physical Review Letters
|January 18, 2018
Summary
In chiral helimagnet MnSi, precursor correlations do not drive the first-order helical transition. Neutron scattering reveals the transition remains sharp under magnetic fields, even as correlations weaken.
Area of Science:
- Condensed Matter Physics
- Magnetism
- Materials Science
Background:
- MnSi is a reference chiral helimagnet and the first system exhibiting Skyrmion lattice correlations.
- The transition to the helimagnetic state at zero magnetic field is of first order.
- Precursor phenomena above T_C involve strong chiral fluctuating correlations.
Purpose of the Study:
- To investigate the role of precursor fluctuating correlations in the first-order helical transition of MnSi under magnetic fields.
- To determine if these correlations drive the transition, as suggested by the Brazovskii scenario.
- To explore the existence of a tricritical point in MnSi.
Main Methods:
- Comprehensive neutron scattering experiments.
- Application of varying magnetic fields up to 0.4 T.
- Analysis of chiral fluctuating correlations and transition order.
Main Results:
- The first-order helical transition in MnSi persists up to 0.4 T magnetic field.
- Chiral fluctuating correlations weaken and align with the field direction above 0.2 T.
- No evidence for a tricritical point was found.
Conclusions:
- The first-order nature of the helical transition is disconnected from the precursor fluctuating correlations.
- The proposed mechanism linking precursor correlations to the first-order transition is not supported by these findings.
- The fundamental nature of the first-order helical transition and precursor phenomena in chiral magnetism remains an open question.
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