Papers by Keyword: Domain Walls

Abstract: Thermal depoling behaviors of (K_0.50Na_0.50)_0.94Li_0.06NbO₃ and (K_0.50Na_0.50)_0.96Li_0.04(Nb_0.85Ta_0.15)O₃ ceramics possessing tetragonal crystalline structure at room temperature have been studied. By comparing the difference in these two compositions during annealing treatment, we provide visual evidence that different types of ferroelectric domain walls play different roles in the thermal depoling. The study results show that the drop in piezoelectric properties can be mainly attributed to the motion of 180^o domain walls below the Curie temperature. When the thermal aging temperature is close to the Curie temperature, the reduction of piezoelectric properties is caused by the movement of 90^o domain walls. The (K_0.50Na_0.50)_0.96Li_0.04(Nb_0.85Ta_0.15)O₃ ceramic with fewer 180^o domains shows very good thermal ageing stability from the low experimental temperature limit of −60 °C up to high temperatures close to T_C.

Abstract: The magnetization dynamics of metal-organic crystals has been studied in low frequency AC magnetic field. Four modes of domain wall motion (Debye relaxation, creep, slide and over - barrier motion (switching)) were distinguished in [Mn^II(H(R/S)-pn)(H₂O)] [Mn^III(CN)₆]⋅2H₂O crystals. Debye relaxation and creep of the domain walls are sensitive to Peierls relief configuration controlled by crystal lattice chirality. Structural defects and periodical Peierls potential compete in the damping of the domain walls. Driving factor of this competition is ratio of the domain wall width to the crystal lattice parameter.

Abstract: The three-dimensional transition structures in the vortex asymmetric domain walls existing in magnetically uniaxial soft magnetic films with in-plane anisotropy are studied by micromagnetic simulations. It is shown that interaction of closely spaced transition structures results in various dynamical scenarios including vortex-antivortex annihilations, creation and annihilation of singular (Bloch) points, and excitation of nonlinear waves.

Abstract: Statistical and multifractal properties of Barkhausen jumps in exchange-coupled ferromagnet/antiferromagnet bilayers are studied on Co/IrMn and NiFe/NiO heterostructures using a magneto-optical indicator film technique. The statistical analysis proves a nonstochastic character of magnetization jumps. In particular, power-law behavior is observed for Co/IrMn samples. Furthermore, the statistics depends on the ferromagnet layer thickness and antiferromagnet layer material structure. The average jump size displays an asymmetry between the forward and backward branches of the hysteresis loop, particularly pronounced for the structure with a thin Co layer. In spite of the observation of such an asymmetry in the activity of the domain nucleation and pinning centers, the statistical distributions of jumps do not show any significant differences for two branches of the hysteresis loop. The conclusion on a nonrandom character of the magnetization process is supported by the multifractal analysis which reveals the presence of correlations in the time arrangement of the Barkhausen jumps.

Abstract: The domain structure dependence on the uniaxial anisotropy constant has been considered in a micrometer-thick film by means of the two-dimensional micromagnetic simulation. The film has both uniaxial and tetra-axial magnetic anisotropies. The new type domain structures and walls caused by the tetra-axial anisotropy presence are predicted.

Abstract: In this paper the contributions of switching, slide, creep and Debye relaxation modes of the domain wall dynamics to the low-frequency magnetic properties of chiral and racemic [Mn^II(HL-pn)(H₂O)][Mn^III(CN)₆]2H₂O molecular ferrimagnets were distinguished.

Abstract: High damping materials exhibiting a loss factor higher than 10-2 are generally considered as polymer or metallic materials. But, it will be interesting to consider ferroelectric or ferrimagnetic ceramics, in which internal friction can be due to the motion of ferroelectric or magnetic domains. High level of internal friction can be obtained in these ceramics in a given temperature range. In the case of ferroelectric ceramics, hard ferroelectrics, such as BaTiO3 or PZT, can show some relaxation peaks below the Curie temperature due the motion of domain walls and the interaction between the domain walls and the oxygen vacancies or cationic vacancies. In the case of ferrimagnetic ceramics, some anelastic manifestations due to the ferrimagnetic domain walls appear below the Curie Temperature TC. These peaks are linked to the interaction of domain walls with cation vacancies or cation interstitials or the lattice. Above the Curie temperature, a relaxation mechanism due to the exchange of cations Mn3+ and their vacancies on octahedral sites should occur.