Magnetic Fluctuations, Precursor Phenomena, and Phase Transition in MnSi under a Magnetic Field

Magnetic Fluctuations, Precursor Phenomena, and Phase Transition in MnSi under a Magnetic Field

Pappas, C. (TU Delft RST/Neutron and Positron Methods in Materials)
Bannenberg, L.J. (TU Delft RST/Neutron and Positron Methods in Materials)
Lelièvre-Berna, E. (Institut Laue-Langevin)
Qian, F. (TU Delft RST/Neutron and Positron Methods in Materials)
Dewhurst, C. D. (Institut Laue-Langevin)
Dalgliesh, R. M. (Rutherford Appleton Laboratory)
Schlagel, D. L. (Iowa State University)
Lograsso, T. A. (Iowa State University)
Falus, P (Institut Laue-Langevin)

2017

The reference chiral helimagnet MnSi is the first system where Skyrmion lattice correlations have been reported. At a zero magnetic field the transition at TC to the helimagnetic state is of first order. Above TC, in a region dominated by precursor phenomena, neutron scattering shows the buildup of strong chiral fluctuating correlations over the surface of a sphere with radius 2π/, where is the pitch of the helix. It has been suggested that these fluctuating correlations drive the helical transition to first order following a scenario proposed by Brazovskii for liquid crystals. We present a comprehensive neutron scattering study under magnetic fields, which provides evidence that this is not the case. The sharp first order transition persists for magnetic fields up to 0.4 T whereas the fluctuating correlations weaken and start to concentrate along the field direction already above 0.2 T. Our results thus disconnect the first order nature of the transition from the precursor fluctuating correlations. They also show no indication for a tricritical point, where the first order transition crosses over to second order with increasing magnetic field. In this light, the nature of the first order helical transition and the precursor phenomena above TC, both of general relevance to chiral magnetism, remain an open question.

http://resolver.tudelft.nl/uuid:3c7cadb4-bbc6-41a1-b71c-e740bf522e7a

https://doi.org/10.1103/PhysRevLett.119.047203

0031-9007

Physical Review Letters, 119 (4)

Institutional Repository

journal article

© 2017 C. Pappas, L.J. Bannenberg, E. Lelièvre-Berna, F. Qian, C. D. Dewhurst, R. M. Dalgliesh, D. L. Schlagel, T. A. Lograsso, P Falus