Crossover behavior of critical helix fluctuations in MnSi

摘要: The critical helix fluctuations in the cubic noncentrosymmetric helimagnet MnSi have been studied by means of neutron small angle scattering and spin echo spectroscopy. To interpret data, analytical formulas for susceptibility real space were obtained first time. calculations presented here are based on theory introduced S. V. Grigoriev et al., Phys. Rev. B 72, 134420 (2005). According to this temperature region can be divided into three parts with different types chiral fluctuations: (i) ferromagnetic like; (ii) isotropic helical; (iii) anisotropic helical ones. increase amplitude a randomly oriented but left-skewed pitch $\mathbf{k}$ upon approaching ${T}_{c}=29\text{ }\text{K}$. scaling law inverse correlation length $\ensuremath{\kappa}$ exhibits crossover at $\ensuremath{\kappa}\ensuremath{\approx}k$. value exponent $\ensuremath{\nu}$ is changed from ${\ensuremath{\nu}}_{1}=0.40(6)$ vicinity ${T}_{c}$ ${\ensuremath{\nu}}_{2}=0.68(1)$ high temperatures. behavior relaxation rate $\ensuremath{\Gamma}$ along easy direction obeys dynamical $\ensuremath{\Gamma}\ensuremath{\sim}{\ensuremath{\kappa}}^{Z}\ensuremath{\sim}{\ensuremath{\tau}}^{Z\ensuremath{\nu}}$ where $\ensuremath{\kappa}\ensuremath{\approx}k$ ${Z}_{1}=2.5(1)$ temperatures ${Z}_{2}=1.10(3)$ close ${T}_{c}$. Fluctuations become 100% left handed point. observed associated dominating influence Dzyaloshinskii-Moria interaction near ${T}_{c}$, responsible ordering.