The Importance of Hysteresis Curves

The magnetic properties of a ferromagnetic substance can be obtained from the size and shape of the hysteresis loop.

(i)    The retentively of soft iron (OC) is greater than that of steel (OC’) i.e., soft iron retains more magnetism than steel, when the magnetizing force is totally removed.

(ii)    The coercive force for soft iron (OD) is smaller than that for steel (OD’), ie., iron is more readily demagnetized than steel.

(iii)    The permeability μ = (B/H) for soft iron is greater than that for steel.

(iv)    The susceptibility χ ( = M/H) for soft iron is greater than that for steel.

(v)    The area of the B – H loop for steel is much larger than that for soft iron. Thus the energy loss per unit volume per cycle of magnetization is greater for steel than that for soft iron.

Choice of Magnetic materials

(i)    Permanent Magnets. Materials used for making magnets are never taken through a cycle. So hysteresis loss is a minor consideration in these cases. These materials should have high retentively and high coercively. So steel is a suitable material for permanent magnets. Recently a number of alloys, having large values of coercivity have been developed for the purpose of construction of permanent magnets. The very suitable alloy of highest coercivity is named as vicalloy (vanadium, iron and cobalt).

(ii)    Electro-magnets. The material for the cores of electromagnets should have maximum flux density with comparatively small magnetizing field and low hysteresis loss. Soft-iron is an ideal material for electro-magnets.

(iii)    Transformer cores. Materials for transformer cores, telephone diaphragms and chokes etc., are frequently subjected to many cycles of magnetization in once second. So the material selected for the purpose must be associated with high magnetic induction and low hysteresis loss. Soft-iron is better than steel for these purposes must be associated with high magnetic induction and low hysteresis loss.
Soft iron is better than steel for these purposes. By alloying soft-iron with 4% silicon, ‘transformer steel’ is produced. It has a higher initial permeability and is an ideal material for cores of transformers. Alloys of iron and nickel, called permalloys have also very large initial permabilities.

(iv)    Ferrites. Their permeability is very high. Ferrites are made by sintering powders consisting of a mixture of ferric oxide and oxides of other metals like lithium, nickel and manganese. Their hysteresis loop is almost rectangular which enables these to be used for memory circuit in computer. These have a high electrical resistivity unlike the ferromagnetic materials which are very good conductors. So ferrites are widely used in the manufacture of components for radio and electrical communication equipments.


 
For more help in The Importance of Hysteresis Curves please click the button below to submit your homework assignment.