Helical spin structure of Mn1−yFeySi under a magnetic field: Small angle neutron diffraction study

Abstract

The magnetic structure of the noncentrosymmetric cubic magnets with Dzyaloshinskii-Moriya interaction Mn1−yFeySi with y=0.0,0.06,0.08,0.10 has been studied by means of the small angle neutron diffraction and magnetization measurements. The compounds order in the spin helix structure below Tc that decreases linearly with the Fe doping and approaches zero at y>0.13. We build the (H-T) phase diagrams for each compound and interpret them on the basis of the Bak-Jensen hierarchical model of the principal interactions. Among these interactions are the spin-wave stiffness that decreases linearly with y, obviously duplicating the change of Tc, and the Dzyaloshinskii interaction showing the moderate evolution with y. It is shown that these compounds undergo the transition from the paramagnetic to helimagnetic phase through the intermediate chiral fluctuating phase. The discussion is given on the comparison of the (T-P) phase diagram in pure MnSi and (T-y) phase diagram of the Mn1−yFeySi compounds showing the role of the principal interactions on the critical temperature Tc of these systems.