5. Domain Observation and Interpretation (126 pages)

5.1 Classification of Materials and Domains

Fig. 5.2:   The reduced anisotropy parameter Q is one of the criteria used to classify magnetic materials and their magnetic microstructures. Other criteria discussed in this section are the manifold of easy axes, and the size, dimension, and surface orientation of a sample

5.2 Bulk High-Anisotropy Uniaxial Materials

Fig. 5.6c:  A high-anisotropy, uniaxial NdFeB crystal containing a twin boundary acts like a mirror to the domain pattern, displaying a branching pattern on the basal plane and on a side plane simultaneously

5.3 Bulk Cubic Crystals

Fig. 5.17b,c:   Domains on an (100)-oriented silicon iron crystal. All visible domains are magnetized parallel to the surface. In (b) this parallel magnetization extends into the depth so that flux closure can be followed in the surface pattern. In the crystal area (c) the perpendicular easy axis is favoured by stress anisotropy, leading to domains apparently meeting head-on on the surface. Almost all domain boundaries in (c) represent V-lines, marking the presence of subsurface perpendicular domains

5.4 Amorphous and Nanocrystalline Ribbons

Fig. 5.47:   A problem in the analysis of domains in metallic glass samples is the presence of ill-defined layered anisotropies. Here they become apparent when a "stress pattern" is found to be embedded in wide basic domains.

5.5 Magnetic Films with Low Anisotropy

p. 448 An overview of the manifold of domain phenomena in thin films. Included in this section are films with in-plane anisotropy, as well as films with weak perpendicular or oblique anisotropy

5.6 Films with Strong Perpendicular Anisotropy

Fig. 5.118a,d,h:   Domains in perpendicular films display spectacular hysteresis phenomena. Applying a perpendicular field, the bubble lattice (a) is transformed into the network pattern (d). Increasing the field further and reducing it again leads to the maze pattern (h)

5.7 Particles, Needles and Wires

Fig. 5.131c-h:   Very small particles can be studies by numerical micromagnetics. Three equilibrium states in a particle with uniaxial anisotropy are shown. The cross section images below demonstrate that (c) is a two-domain state, while (d) and (e) are different variants of three-domain states

5.8 How Many Different Domain Patterns?

In this section, it is argued that the manifold of domain patterns is inexhaustible, and new, hitherto unknown domain patterns can be found every day. There are good arguments for continued efforts in domain analysis, however, as we conclude:

"It is hoped that the presented gallery of domain patterns and magnetization processes in ideal samples can help in the understanding of patterns and processes in disturbed samples or in samples of different symmetry or shape. Every domain pattern that is correctly analysed and understood in one case, can serve as a clue to patterns in related cases."