Magnetic domains:
1. Weiss proposed this concept of Domains in 1907 to explain the hysteresis effects observed in ferromagnetic materials as well as to explain the properties of Ferromagnetic materials.
2. A region in a ferromagnetic material where all the magnetic moments are aligned in the same direction is called a domain. A magnetic domain is completely magnetized and has definite boundaries. So a ferromagnetic material is divided up into these small regions, called domains, each of which is at all times completely magnetized.
3. The direction of magnetization, however, varies from domain to domain and thus the net macroscopic magnetization is zero in a virgin specimen in the absence of external magnetic field.
4. But when the ferromagnetic material is in the magnetic field, in the initial stages of magnetization in the material, the domain having moments parallel magnetic fields increases in area; in the final saturation stage, the other domains are rotated parallel to the field.
5. Similarly if we demagnetize the material the regular domain arrangement is changed and it is different from the original state. This creates the hysteresis in the ferromagnetic substances.
Further this theory can explain the following;
1. If a magnet is broken into pieces, each piece will be a magnet with a north and a south pole. This is because the domains continue to remain in broken pieces.
2. A magnet heated or roughly handled tends to lose its magnetism. This is because the alignment of the domains in the magnet is likely to be disturbed during heating and rough handling. Hence magnetism is reduced or lost.
3. Domains of soft iron are easily rotated with a comparatively small magnetizing force and hence they are very easily magnetized or demagnetized. In this case of steel a large force is required for rotating the domains which explains the high retentivity of that material.
4. A specimen when magnetized suddenly experiences a slight change in its length which is due to rearrangement of domains inside. This is called magnetostriction.,
5. Processes of domain magnetization
There are two possible ways to align a random domain structure by applying an external magnetic field.
1. Weiss proposed this concept of Domains in 1907 to explain the hysteresis effects observed in ferromagnetic materials as well as to explain the properties of Ferromagnetic materials.
2. A region in a ferromagnetic material where all the magnetic moments are aligned in the same direction is called a domain. A magnetic domain is completely magnetized and has definite boundaries. So a ferromagnetic material is divided up into these small regions, called domains, each of which is at all times completely magnetized.
3. The direction of magnetization, however, varies from domain to domain and thus the net macroscopic magnetization is zero in a virgin specimen in the absence of external magnetic field.
4. But when the ferromagnetic material is in the magnetic field, in the initial stages of magnetization in the material, the domain having moments parallel magnetic fields increases in area; in the final saturation stage, the other domains are rotated parallel to the field.
5. Similarly if we demagnetize the material the regular domain arrangement is changed and it is different from the original state. This creates the hysteresis in the ferromagnetic substances.
Further this theory can explain the following;
1. If a magnet is broken into pieces, each piece will be a magnet with a north and a south pole. This is because the domains continue to remain in broken pieces.
2. A magnet heated or roughly handled tends to lose its magnetism. This is because the alignment of the domains in the magnet is likely to be disturbed during heating and rough handling. Hence magnetism is reduced or lost.
3. Domains of soft iron are easily rotated with a comparatively small magnetizing force and hence they are very easily magnetized or demagnetized. In this case of steel a large force is required for rotating the domains which explains the high retentivity of that material.
4. A specimen when magnetized suddenly experiences a slight change in its length which is due to rearrangement of domains inside. This is called magnetostriction.,
5. Processes of domain magnetization
There are two possible ways to align a random domain structure by applying an external magnetic field.
- By the motion of domain walls: i.e., by an increase in the volume of domains that are favourably oriented with respect to the magnetizing field at the cost of those that are unfavourably oriented as shown in figure 4.4(b); figure4.4 (a) shows that arrangements of domains for zero resultant magnetic moment in a single crystal or virgin specimen when there is no applied magnetic field.
- By rotation of domains: i.e., by the rotation of the direction of magnetization of domain along the direction of field as shown in figure 4.4(c). In weak magnetizing fields, he magnetizing of the specimen is due to the motion of domain walls and in stronger fields that is due to the rotation of domains.
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