Field-induced reorientation of helix in MnSi near TC

The spiral structure of the single crystal MnSi has been studied by SANS near T-C = 29K in the magnetic field. When the field (H > 20 mT) is applied along one of the < 111 > axes, it produces a single domain sample with the helix wave vector along the field. The 90 degrees-reorientation of the spin spiral from the [111] axis to [1-10] axis is observed in the field range from 130 to 180 mT in close vicinity to T-C. Further increase of the field above H = 180 mT, restores the original orientation of the helix and leads to the induced ferromagnetic state at H = 350 mT. The SANS experiments demonstrate that not a new phase, but helix reorientation occurs in the narrow domain of the H-T phase diagram near T-C. (c) 2006 Elsevier B.V. All rights reserved.