Abstract
We have studied in detail the A-phase region in the field-temperature (H-T) phase diagram of the cubic heli-magnet MnSi using small angle neutron diffraction. The A-phase revealed itself as a two-dimensional hexagonal pattern of Bragg spots with k h(1, 2, 3) ⊥ H. The directions and magnitudes of the wave vectors k h(1, 2, 3) are well preserved over the whole crystal of the size of 100 mm3, but in the small room of the (H-T) phase diagram just below T c = 29 K. The droplets of the orientationally disordered, presumably hexagonal, spin structure with k h ⊥ H are observed in the wide range beyond the A-phase boundaries in the field range from B T1 ≈ 0.1 T to B T2 ≈ 0.25 T at temperatures down to 15 K. No melting of these droplets into individual randomly located skyrmions is observed for all temperatures and magnetic fields. The wave vector of two-dimensional modulations k h is equal to the wave vector of the cone phase k c . We conclude that observable is a two dimensionally modulated hexagonal spin superlattice built on the same competition of interactions (ferromagnetic exchange and Dzyaloshinskii-Moriya interactions) similar to a case of one-dimensionally modulated simple spin spiral.
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Grigoriev, S.V., Potapova, N.M., Moskvin, E.V. et al. Hexagonal spin structure of A-phase in MnSi: Densely packed skyrmion quasiparticles or two-dimensionally modulated spin superlattice?. Jetp Lett. 100, 216–221 (2014). https://doi.org/10.1134/S0021364014150065
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DOI: https://doi.org/10.1134/S0021364014150065