Generation and gyroscopic quasi-relativistic dynamics of antiferromagnetic vortices in domain walls of yttrium orthoferr
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Generation and Gyroscopic Quasi-relativistic Dynamics of Antiferromagnetic Vortices in Domain Walls of Yttrium Orthoferrite M. V. Chetkin, Yu. N. Kurbatova, T. B. Shapaeva, and O. A. Borshchegovskiœ Moscow State University, Vorob’evy gory, Moscow, 119992 Russia e-mail: [email protected] Received November 14, 2005
Abstract—An unusual nonlinear relation between the velocity of an antiferromagnetic (AFM) vortex along a domain wall (DW) on the DW velocity is detected. This relation has a maximum whose position depends on the topological charge of the vortex. As the DW velocity increases from the value corresponding to the maximum to its limiting value, the AFM-vortex velocity decreases and tends to zero. The total AFM-vortex velocity increases nonlinearly with the DW velocity and levels off at 20 km/s, which is equal to the velocity of spin waves in the linear section of their dispersion law. The experimental data are approximated satisfactorily. The dynamics of AFM vortices in DWs of yttrium orthoferrite, just as the dynamics of the DWs, is quasi-relativistic and gyroscopic. PACS numbers: 75.60.Ch DOI: 10.1134/S106377610607017X
1. INTRODUCTION The dynamics of topological magnetic solitons, namely, domain walls (DWs) and vertical Bloch lines (VBLs), or antiferromagnetic vortices in DWs of orthoferrites, differs substantially from the well-known results for other ferromagnets. The dynamics of topological magnetic solitons in orthoferrites is, first, supersonic dynamics, which has not been detected experimentally in any magnetically ordered materials [1, 2], and, second, quasi-relativistic dynamics with the limiting velocity that is equal to the velocity of spin waves in the main linear section of their dispersion law [3–6]. The latter dynamics has not been observed either. In orthoferrites exhibiting the Dzyaloshinskiœ–Moriya interaction, low magnetic fields can be used to control domain-wall motion and, thus, antiferromagnetic-vortex motion. This is impossible in antiferromagnets. As the magnetic field increases, the DW velocity in orthoferrites increases first linearly and then nonlinearly and levels off at 20 km/s, which is the limiting velocity. This is the maximum velocity of topological magnetic solitons that has been reached to date. The subsonic and supersonic DW velocities in orthoferrites were studied by the Sixtus–Tonks technique [2]. The modification of this technique with two light spots sequentially intersected by a moving DW allowed one to experimentally find the limiting DW velocity for the first time and to interpret it as the velocity of spin waves in the main linear section of their dispersion law [1, 3]. A theory for the quasi-relativistic dynamics of DWs in orthoferrites was developed in [7]. The Landau–Lifshitz equa-
tions were solved for a moving DW with antiferromagnetism (l) and weak-ferromagnetism (m) vectors rotated in the ab plane. A theory for the quasi-relativistic dynamics of DWs in orthoferrites was also developed in [8]. The Lagrangian for these crystals was obtained in [9]; it conta
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