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

Abstract

The reference chiral helimagnet MnSi is the first system where skyrmion lattice correlations have been reported. At zero magnetic field the transition at $T_C$ to the helimagnetic state is of first order. Above $T_C$, in a region dominated by precursor phenomena, neutron scattering shows the build up of strong chiral fluctuating correlations over the surface of a sphere with radius $2\pi /\ell$, where $\ell$ 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 $T_C$, both of general relevance to chiral magnetism, remain an open question.

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• Reorientations, relaxations, metastabilities and multidomains of skyrmion lattices
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• Weak crystallization of fluctuating skyrmion textures in MnSi
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• Exploring the origins of the Dzyalloshinski-Moria interaction in MnSi
• Skyrmions and spirals in MnSi under hydrostatic pressure
• Evolution of helimagnetic correlations in Mn${}_{1-x}$Fe${}_x$Si with doping: a small-angle neutron scattering study
• Single helicity of the triple-$q$ triangular skyrmion lattice state in cubic chiral helimagnet EuPtSi
• Time of Flight Modulation of Intensity by Zero Effort on Larmor
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• Stability of the skyrmion lattice near the critical temperature in cubic helimagnets
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• Search for pressure-induced tricriticality in Cr