Experimental evaluation of the orbital angular momentum in hexagonal chiral magnet MnNb3S6: Comparison with hexagonal CrNb3S6 and cubic MnSi

Abstract

Monoaxial chiral magnet MnNb3S6 exhibits long-time relaxation of magnetization owing to the slow velocity of solitons in the chiral soliton lattice state, whereas the contrasting chiral magnet CrNb3S6 exhibits fast magnetization relaxation owing to fast soliton velocity. In general, the velocity of solitons stabilized at dc magnetic field depends on the magnitude of the Dzyaloshinskii–Moriya (DM) interaction. This study evaluated the ratio of the orbital magnetic moments morb to their spin counterparts mspin, morb/mspin, related to the magnitude of the DM interaction for MnNb3S6 using soft x-ray magnetic circular dichroism spectroscopy experiments. The |morb/mspin| value of less than 1% for MnNb3S6 was compared with those of the hexagonal CrNb3S6 and cubic chiral magnet MnSi. The x-ray absorption spectrum of MnNb3S6 with a small DM interaction originates from a small amount of Mn3+ and the main valence Mn2+, whereas the valences of MnSi are Mn0, dominant Mn+, and Mn2+. Consequently, the morb/mspin value for MnNb3S6 was determined to be less than one-tenth of that for MnSi. We must discuss the magnitude of the DM interaction in compounds, including Mn, considering the valence of Mn as well as the crystal structure.