ИСТИНА

It was shown experimentally that under sharp braking of a segment of the yttrium orthoferrite domain wall (DW) moving with supersonic velocity (12 km/s) a pair of solitary deflection waves appears. These waves have equal amplitudes and move with equal velocities in opposite directions along the DW. These solitary deflection waves accompany antiferromagnetic (AFM) vortices. These vortices are generated inside the DW and move along it. The existence of antiferromagnetic vortices in the yttrium orthoferrite DW was predicted theoretically by Farztdinov et al. [1]. The two-fold high-speed photography method with sub-nanosecond resolution was used to study these vortices dynamics. [2] From one photo of the dynamic DW with a fine structure this method allows to determine the DW velocity – v, the velocity of solitary deflection wave along the DW – u, the total velocity of this wave – w, its amplitude – a, tilt angle of the leading edge of this wave – φ and its existence time. According to experiment at fixed DW velocity the solitary deflection wave velocity along the DW, the wave amplitude and the tilt angle of the leading edge of this wave almost unchanged over time. The curve w(v) demonstrates nonlinearly increase and saturation on the level 20 km/s. This value is a limiting DW velocity equals to the spin waves velocity on the linear part of their dispersion low. The increase of w(v) dependence is sharper for solitary deflection waves with smaller amplitudes. At fixed DW velocity the solitary deflection wave with greater amplitude moves with smaller velocity along the DW. The dependence φ(a) is nonlinear. For small amplitude values the angle φ linearly increases. For a≈10 μm φ≈30–35o, as amplitude increases to 18 μm angle φ doesn’t change. Subsequent increasing of the wave amplitude leads to decreasing of φ. Solitary deflection waves accompanying AFM vortices move along the supersonic part of the DW. The transition from sonic to supersonic motion of the orthoferrite DW happens very rapidly. [3] It can be seen experimentally as one part of the DW still moves with the sound velocity (4 km/s) another one moves with supersonic velocity (12 km/s). The solitary deflection waves accompanying AFM vortices move along the supersonic part of the DW. It was shown that angle φ decreases and tends to zero if the distance between solitary deflection wave and sound part of the DW decreases. This fact suggests that inside DW moving with velocity less or equal to sound velocity there are no AFM vortices. In work [4] the theoretical simulation results of the AFM vortices dynamics in the DW of yttrium orthoferrite were compared with experimental data. Qualitative agreement between theory and experiment is observed only at the DW velocity greater than 12 km/s. [1] M.M. Farztdinov, M.A. Shamsutdinov, A.A. Khalfina. Fiz.Tverd. Tela, 21 (1979) 1522-1527. [2] M.V.Chetkin, Yu.N.Kurbatova, T.B.Shapaeva. JMMM, 321 (2009) 800-802. [3] V.G. Bar'jakhtar, M.V. Chetkin, B.A. Ivanov, S.N. Gadetskiy, Dynamics of Topological Magnetic Solitons. (Springer tracts in modern physics, Berlin), vol. 129, 1994. [4] M.V.Chetkin, Yu.N.Kurbatova, T.B.Shapaeva. JMMM, 324 (2012) 3576-3578.