Critical behavior of the single-crystal helimagnet MnSi.

The critical behavior of the single-crystal helimagnet MnSi is investigated by means of bulk dc magnetization at the boundary between the conical state and paramagnetic phase. We obtain the critical exponents (β = 0.242 ± 0.006, γ = 0.915 ± 0.003, and δ = 4.734 ± 0.006), where the self-consistency and reliability are verified by the Widom scaling law and the scaling equation. The critical exponents of MnSi belong to the universality class of tricritical mean-field theory, which unambiguously indicates a tricritical phenomenon at the boundary between the first-order phase transition and the second-order one induced by the external magnetic field. The tricritical point (TCP) is determined as HTCP ≈ 3200 Oe at the critical temperature, consistent with the previous report [A. Bauer, M. Garst, and C. Pfleiderer, Phys. Rev. Lett. 110, 177207 (2013)]. The critical behavior suggests a long-range magnetic coupling with the exchange distance decaying as J(r) ≈ r -4.3 in MnSi. [ABSTRACT FROM AUTHOR]