Magnetic Properties of Engineering MaterialsPublished on 24/2/2012 and last updated on 1/9/2018
- Retentivity or Magnetic Hysteresis
- Coercive force
PermeabilityIt is the property of magnetic material which indicates that how easily the magnetic flux is build up in material. Some time is also called as the magnetic susceptibility of material. It is determined by the ratio of magnetic flux density to magnetizing force producing this magnetic flux density. It is denoted by µ. Hence, μ = B/H. Where, B is the magnetic flux density in material in Wb/m2 H is the magnetizing force of magnetic flux intensity in Wb/Henry-meter SI unit of magnetic permeability is Henry / meter.
Permeability of material is also defined as, μ = μ0 μr Where, µ0 is the permeability of air or vacuum, and μ0 = 4π × 10-7 Henry/meter and µr is the relative permeability of material. µr = 1 for air or vacuum. A material selected for magnetic core in electrical machines should have high permeability, so that required magnetic flux can be produced in core by less ampere- turns.
RetentivityWhen a magnetic material is placed in an external magnetic field, its grains get oriented in the direction of magnetic field. Which results in magnetization of material in the direction of external magnetic field. Now, even after removal of external magnetic field, some magnetization exists, which is called residual magnetism. This property of material is called Magnetic retentively of material. A hysteresis loop or B-H cure of a typical magnetic material is shown in figure below. Magnetization Br in below hysteresis loop represents the residual magnetism of material.