22 April 2011

Differences between Hard and Soft Magnetic Materials

Hard Magnetic Materials
Soft Magnetic Materials
Materials which retain their magnetism and are difficult to demagnetize are called hard magnetic materials.
These materials retain their magnetism even after the removal of the applied magnetic field. Hence these materials are used for making permanent magnets. In permanent magnets the movement of the domain wall is prevented. They are prepared by heating the magnetic materials to the required temperature and then quenching them. Impurities increase the strength of hard magnetic materials.
Soft magnetic materials are easy to magnetize and demagnetize.
These materials are used for making temporary magnets. The domain wall movement is easy. Hence they are easy to magnetize. By annealing the cold worked material, the dislocation density is reduced and the domain wall movement is made easier. Soft magnetic materials should not possess any void and its structure should be homogeneous so that the materials are not affected by impurities.
They have large hysteresis loss due to large hysteresis loop area.
They have low hysteresis loss due to small hysteresis area.
Susceptibility and permeability are low.
Susceptibility and permeability are high.
Coercivity and retentivity values are large.
Coercivity and retentivity values are less.
Magnetic energy stored is high.
Since they have low retentivity and coercivity, they are not used for making permanent magnets.
They possess high value of BH product.
Magnetic energy stored is less.
The eddy current loss is high.
The eddy current loss is less because of high resistivity.