Thermal expansion and magneto-volume studies of the itinerant helical magnet MnSi

Abstract

Thermal expansion and forced magnetostriction of MnSi were measured as a function of temperature down to 5 K and magnetic field to 3 T. The small length (volume) discontinuity at the magnetic phase transition in MnSi decreases with application of magnetic field to a value $\Delta L/L\sim 10^{-7}$, and then suddenly the discontinuity seemingly jumps to zero. Thermal expansivity peaks strongly deteriorate with magnetic fields. No specific features identifying a tricritical point were observed. We propose that the Frenkel concept of heterophase fluctuations may be relevant in the current case. Therefore, we suggest that the magnetic phase transition in MnSi always remains first order at any temperature and magnetic field, but the transition is progressively smoothed by heterophase fluctuations. These results question the applicability of a model of a fluctuation-induced first order phase transition for MnSi. Probably a model of coupling of an order parameter with other degrees of freedom is more appropriate.

6 figures, 5 pages

References in corpus (3)

• Fluctuation-induced first-order phase transition in Dzyaloshinskii-Moriya helimagnets
• Ultrasonic studies of the magnetic phase transition in MnSi
• Inexhaustible physics of the helical magnet MnSi: field evolution of the magnetic phase transition inferred from ultrasound studies

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