Hysteresis

Hysteresis occurs in a system which includes a magnetic field. Hysteresis is a common property of ferromagnetic substances. When the magnetization of a ferromagnetic substance lags behind the magnetic field, this effect can be generally referred to as the hysteresis effect.

Hysteresis Loop

A hysteresis loop (also mentioned as a hysteresis curve) is a four-quadrant diagram showing the relationship between induced magnetic flux density (intensity of magnetisation) B and magnetizing force H.

Hysteresis loop is produced by determining the magnetic flux which is coming out from ferromagnetic material during the changing of the external field of magnetization.

• Intensity of magnetism (B) increases if the magnetic field (H) is raised from 0 (zero).
• When the magnetic field increases, the value of magnetism also increases and at last reaches a point known as saturation point where intensity of magnetisation is constant.
• When the value of the magnetic field decreases, the value of magnetism also decreases. The point at which B (Intensity of magnetism) and H (magnetic field) are equal to zero, material retains some amount of magnetism, which is called residual or retentivity magnetism.
• When the magnetic field decreases towards the negative side, the magnetism of the material also decreases.
• Force which is needed to remove the retentivity of a material is called Coercive force (C).
• Cycle is continued in opposite direction
• Because of the opposite and forward direction process, the cycle is completed and this cycle is termed as hysteresis loop.

Advantages of Hysteresis Loop

1. Small area of the hysteresis loop shows small loss of Hysteresis. 
2. The hysteresis loop provides a material with the significance of coercivity and retentivity. Therefore, choosing the right material to make a permanent magnet is simplified by the heart of machines.
3. B-H graph is used to evaluate residual magnetism, selecting a material for electromagnets.

Retentivity

Retentivity is the amount of magnetism which remains after the external magnetic field has been removed. Retentivity is defined as a material’s ability to retain certain magnetic properties after an external magnetizing force has been removed.

Coercivity

The amount of magnetic field (H) which is needed to drive the intensity of magnetism (B) to the zero line gives a value for the Coercivity of the substance. Coercivity is also termed as Coercive Strength. Coercivity of a substance is the resistance to changes in magnetization.  The coercivity of soft magnetic materials is low Coercivity and high for hard magnetic materials.

Energy Loss due to Hysteresis

The largest example of the analysis of energy loss due to hysteresis is a transformer, as the energy is needed along the magnetization and demagnetization processes.

Energy expands during magnetization and demagnetization of magnetic materials and this extended energy manifests itself as heat. The term used for this type of heat loss is hysteresis loss.

Due to the continuous process of magnetization and demagnetization in transformers, the energy is constantly being lost in the form of heat, which reduces the efficiency of the transformer. 

Soft iron cores are used in transformers to avoid energy losses, since the energy loss or hysteresis losses are significantly lower with soft iron than with other materials.

Types of Hysteresis

There are two types of hysteresis which are given here.

1. Rate Dependent Hysteresis
2. Rate Independent Hysteresis

Conclusion

Hysteresis occurs in a system which includes a magnetic field. Hysteresis is a common property of ferromagnetic substances.

A hysteresis loop (also mentioned as a hysteresis curve) is a four-quadrant diagram showing the relationship between induced magnetic flux density (intensity of magnetisation) B and magnetizing force H.

Intensity of magnetism (B) increases if the magnetic field (H) is raised from 0 (zero).

When the magnetic field decreases towards the negative side, the magnetism of the material also decreases.

Retentivity is the amount of magnetism which remains after the external magnetic field has been removed. Retentivity is defined as a material’s ability to retain certain magnetic properties after an external magnetizing force has been removed.

The amount of magnetic field (H) which is needed to drive the intensity of magnetism (B) to the zero line gives a value for the Coercivity of the substance.

There are two types of hysteresis which are given here.

1. Rate Dependent Hysteresis
2. Rate Independent Hysteresis