Magnetic domain wall motion

Figure 6 Scanning Karr image of the magnetization changes in the indirection for a thin-film head having a 1-MHz, 5-mA p-p coil current, and the magnetic domain pattern deduced for this head from the observed domain wall motion. ...

In dielectric materials there can be both permanent and induced polarization domains. The walls between these domains may also act as barriers to dislocation motion. They tend to have larger energies than magnetic domain walls so they may have more effect on hardness (McColm, 1990). 

Figure 20.1. The magnetization process (a) demagnetized state (b) unsaturated state (c) saturated state. When an external magnetic field is applied, domain rotation and domain wall motion occur simultaneously or sequentially. Domain configuration can be found by minimizing the total energy related to magnetization. (From Ref 1, with permission from Elsevier.)...

A metallic glass containing 80% Fe and 20% B is an excellent soft magnetic material because there are no grain boundaries to obstruct domain wall motion. 

When the field is removed, there is a resistance to domain wall motion preventing reorientation of the domains. As a result there is a residual magnetization, known as remanence (Br), and the material acts as a permanent magnet. 

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