Hexagonal spin structure of A-phase in MnSi: Densely packed skyrmion quasiparticles or two-dimensionally modulated spin superlattice?

Grigoriev, S.; Potapova, N.; Moskvin, E.; Dyadkin, V.; Dewhurst, Ch.; Maleyev, S.

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. The directions and magnitudes of the wave vectors k are well preserved over the whole crystal of the size of 100 mm, but in the small room of the ( H- T) phase diagram just below T = 29 K. The droplets of the orientationally disordered, presumably hexagonal, spin structure with k ⊥ H are observed in the wide range beyond the A-phase boundaries in the field range from B ≈ 0.1 T to B ≈ 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 is equal to the wave vector of the cone phase k. 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.

SKYRMIONS; QUASIPARTICLES; SUPERLATTICES; CRYSTAL structure; MAGNETIC fields

JETP Letters, 2014, Vol 100, Issue 3, p216

0021-3640

Academic Journal

10.1134/S0021364014150065