These lecture notes aim at introducing the main concepts underlying magnetic domain and wall physics. Emphasis is laid on soft magnetic materials, i.e. materials which, in the bulk state, are essentially magnetically isotropic, although most of the phenomenology remains general. Besides, magnetization dynamics and its consequences on domain wall state transformations are not treated in this chapter. The text is divided into nine sections. Section 2 depicts the various energy terms to be considered within the micromagnetic approach which treats the magnetization as a continuous Maxwell field whereas energy minimization in the general case is treated in Section 5, leading to the basic static equilibrium equations governing the distribution of magnetization inside a magnetic body. The question of the motive force behind decomposition into domains and domain geometry is addressed in Sections 4, 6 and 7. The former briefly pinpoints the magnetostatic energy reduction stemming from a decomposition of the magnetized volume into domains. The latter describes in detail the domain configuration to be expected from anisotropy-free soft magnetic elements with a basically two-dimensional in-plane magnetization distribution, and offers several illustrations of the elegant geometrical construction due to Van den Berg. It also provides an introduction to quasi-singular magnetization distributions in soft ferromagnets. Section 6, devoted to the nucleation of stripe domains, provides one example of the use of the general equilibrium equations in the vicinity of saturation. The rather involved issue of domain wall structures is considered in Sections 8, 9 and 10. A comprehensive treatment of one-dimensional wall structures expected to occur in bulk materials will be found in the first of these three sections, whereas the second is concerned with those specific domain wall structures to be found at intermediate thicknesses and in the half-space. Wall sub-structures, namely lines, are briefly alluded to. Section 10 is also devoted to the fast growing field of magnetic artificial structures with dipolar and exchange inter-layer interactions. Lastly, intrinsic coercivity mechanisms are described in Sections 3 and 11, starting with Stoner-Wohlfarth hysteresis in thin films and ending with some manifestations of the more intricate topological hysteresis, i.e. those hysteretic phenomena associated with noncontinuous transformations of the magnetization distribution.
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- Domains and Domain Walls in Soft Magnetic Materials, Mostly
- Springer Netherlands
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