Magnetic Domains and the Hysteresis Curve

The situation is not unlike grain boundaries in a polycrystalline material, with the important distinction that whereas a polycrystalline solid will always attempt to eliminate these areas of excess energy, in a magnetic material an equilibrium is established. 

The relationship between the existence of domains and hysteresis is shown in Fig. 15.7. The dependence of A/ on // for a virgin sample is shown in Fig. 15.7a. What occurs at the microscopic level is depicted in Fig. 5.1h 

At low fields, the movement of the domain walls is very much like an elastic band (or a pinned dislocation line) that stretches reversibly. If the field is removed at that point, the unloading curve is coincident with the loading curve and the process is completely reversible. 

Upon the removal of H, M does not follow the original curve, but instead follows the line and intersects the Y axis at the point labeled 

In order to completely rid the material of its remnant magnetization, the polarity of the magnetizing field has to be reversed. The value of H at which M goes to zero is called the coercive magnetic field intensity (Fig. 15.8 ). 

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