When a magnetic material is placed in an external magnetic field, its grains get oriented in the direction of the magnetic field. Which results in the magnetization of a material in the direction of an external magnetic field. Now, even after the removal of the external magnetic field, some magnetization exists, which is called residual magnetism. This property of a material is called Magnetic retentively of material.
• The units in which the retentivity of a material is measured is weber per square meter.
Due to the retentivity of material, even after the removal of an external magnetic field, some magnetization exists in the material. This magnetism is called residual magnetism of material. To remove this residual magnetization, we have to apply some external magnetic fields in opposite direction. This external magnetic motive force (ATs) required to overcome the residual magnetism is called the “coercive force” of material. In the above hysteresis loop -Hc represents the coercive force.
• The units in which coercivity is measured is ampere per meter and denoted as overset. It’s also known as coercive force or coercive field.
NOTE: In the BH curve of the hysteresis loop of material then the point at which the magnitude of H is zero and B on the Y-axis then, this point on B is called the retentivity of a material. Similarly, In the BH curve of the hysteresis loop, the point on the negative X-axis where the magnitude of B is zero and has some defined value on H, this value of H is called coercivity of a material.
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