The spin chirality in MnSi single crystal probed by small angle scattering with polarized neutrons

Abstract

The weak itinerant ferromagnet MnSi orders with a left-handed helical spin structure below T C=29 K. The helicity with a vector m=[ S 1 × S 2]/S 2 along the crystallographic axis [1 1 1] is realized by an antisymmetric Dzyaloshinski–Moriya interaction. The small angle diffraction study with polarized neutrons on a single MnSi crystal was performed within the temperature range from 10 K to T C and the magnetic field B from 1 to 350 mT. The single crystal was oriented in such a way that two axes [1 1 1] and [1 1 −1] were set in a plane perpendicular to the incident beam. Four major diffraction peaks at ± q 1 and ± q 2 along the axes and four minor peaks at q=± q 1± q 2 were observed. The intensity I p= I(+ P 0)+ I(− P 0), the polarization P p=[ I(+ P 0)− I(− P 0)]/ I p and the position q p of the peaks were measured as a function of the temperature and the magnetic field. From intensity of the peaks the chiral critical exponent is obtained as β=0.47±0.04.