Dynamics of domain walls in orthoferrites in the light of results obtained for ferrite-garnet films

Abstract

538.61Results obtained for monocrystalline films of ferrite-garnets (FGMFs) are used to explain why the generation of microdomains ahead of a moving domain wall (DW) has been observed for orthoferrites in experiments involving the dynamic growth of multiple domains but has not been seen in experiments in which the motion of an isolated DW was studied. The explanation is based on the dependence of the dimensionless decay parameter on the constant magnetic field applied in the plane of the film (plate).L. P. ] observed a new mechanism of motion of DWs in an experimental study of the dynamic growth of cylindrical and band-like magnetic domains in an FMGF with the (1 11) orientation under the influence of an impulsive magnetic field lip applied along a normal to the plane of the film. The essence of the mechanism is that when the strength of the impulsive field exceeds the critical strength Hp, nonuniform rotation of magnetization causes local sections of a moving DW to generate microdomains ahead of it. These microdomains were referred to as magnetic perturbations in [1--4]. The microdomains subsequently increase in size and, generating new magnetic perturbations around themselves, merge with the original domain.The phenomenon of microdomain formation ahead of a moving DW was also observed in [5][6][7][8][9][10][11][12] in the case when the material was initially uniformly magnetized (a constant magnetic bias field Hb was applied). Study of a large number of specimens revealed that microdomains are nucleated only in FMGFs having a low value for the Gilbert decay parameter tx, and no microdomains are seen at ~ > 0.15. It was concluded on this basis that microdomain formation is a purely dynamic phenomenon and that it is suppressed by dissipative processes with a short relaxation time.In [6] we advanced the hypothesis, later proven by experiments in [7], that the local rotation of magnetization ahead of a moving DW, loading to the generation of microdomains, is caused by spin waves (SWs) radiated by the moving DW [13]. Spin waves are the magnetic perturbations responsible for destabilizing the magnetization vector ahead of moving DWs and thereby causing their local rotation. In our opinion, the same effect can also cause moving DWs to emit not only magnons, but also other quasi-particles (such as phonons).It was established that the local rotation of magnetization in front of a moving DW is a universal mechanism of its motion when the acting magnetic field exceeds a certain threshold which is proportional to the uniaxial magnetic anisotropy field HK. The mechanism is operative in all uniaxial FMGFs, the dimensionless decay parameter of which changes from infinitesimal values to ot > 1 [11]. The main difference in the manifestation of this mechanism in films with different values of t~ is that the width of the region occupied by the rotation of magnetization decreases with an increase in the dimensionless decay parameter. Thus, at a certain value of ct, it becomes impossible for microdomains to be generated in front of...