Spin chirality in a MnSi single crystal from small-angle scattering of polarized neutrons

摘要

The cross section of small-angle neutron scattering from a noncentrosymmetric cubic MnSi crystal (with a helicoidal spin structure with left-handed rotation of the helix and the helix wave vector Q formed below T-C approximate to 29 K) has been studied as a function of polarization P-0, magnetic field B, and temperature T The measurements were made in a magnetic field B ranging from 10 to 3500 Oe in the temperature range (10-60) K. At T < T-C, where T-C = (28.70 +/- 0.05) K, Four Bragg diffraction peaks were observed at the momenta +/-q(c1) and q(c2), whose directions coincided with the [111] and [111] axes, respectively. The polarization intensity and the positions q(p) of these peaks are measured as functions of T and B, and the temperature dependence of the helix period is determined. The critical chirality index beta(c) is found to be equal to 0.47 +/- 0.04. In the applied magnetic field, the q(p) directions are rotated toward the direction of the field B and remain parallel to this field in the fields B > 1500 Oe. With a decrease in the field B, an unusual magnetic hysteresis was observed. (C) 2004 MAIK "Nauka/Interperiodica".