The document discusses domain theory of ferromagnetism and hysteresis. It first defines key terms like ferromagnetism, domains, and hysteresis. It then explains that in ferromagnetic materials below the Curie temperature, the material consists of magnetic domains that are spontaneously magnetized in random directions. When an external magnetic field is applied, the domains begin to align with the field. This leads to hysteresis, where the magnetic flux density B lags behind changes in the applied magnetic field H, forming a hysteresis loop on the B-H graph. The size of the hysteresis loop depends on the number of domains switching direction as the field changes.

1. Domain Theory of
Ferromagnetism and
Hysteresis
Makwana Nikhil N. – 150110109022
Makwana Rahil – 150110109023
Manavar Vatsal A. - 150110109024

2. Contains
Basic details of Domain
Effect of External Magnetic Field on
the Domains
Step by step magnetization
Details about Hysteresis
Explanation of Hysteresis on the Basis
of Domain Theory

3. Terminologies
 FERROMAGNETISM:
“Ferromagnetism is a phenomenon in which a
material gets magnetized to a very large extent in the presence of an
external field.”
 DOMAIN:
“A specimen of ferromagnetic material consists of different
region which are spontaneously magnetized below the Curie temperature.
These spontaneously magnetized or self magnetized regions in a
ferromagnetic material is called the domains.”
 HYSTERESIS:
“Hysteresis is lagging (phase lagging) of magnetic
induction B in ferromagnetic and ferrimagnetic materials with respect to
the cyclic variation of an applied magnetic field, when the specimen is at a
temperature below its Curie temperature.”

4. DOMAINS
 At the lower temperature than Curie, & in the absence of
an external magnetic field, the direction of magnetization
of each domain have random orientation in space as shown
in figure.

5. Effect of external magnetic
field on Domain
 As we know that when there is no any external field
applied to the material, all the domain of the ferromagnetic
material are in random direction itself.

6. Continued…
But when the external magnetic field is
applied to any ferromagnetic material, its
domain tends to get aligned in the direction
of the external field.

7. Continued…
 As the external magnetic field becomes stronger, all the
domains gets completely aligned in the direction of the
external magnetic field.

8. Hysteresis
As we have earlier seen that the “Hysteresis
is lagging (phase lagging) of magnetic
induction B in ferromagnetic and
ferrimagnetic materials with respect to the
cyclic variation of an applied magnetic field,
when the specimen is at a temperature
below its Curie temperature.”
It is the graph of Magnetic flux density (B)
versus magnetic field (H).
It is also known as hysteresis curve.

9. Hysteresis Curve
Br
OHc
A
C

10. Explanation
 As we increase magnetic field H, value of B also increases and the
curve develops along Oa. At a, if H is further increases, B remains
constant. If H is done 0, then value of Ob at point b is called the
RETENTIVITY.
 Now when the value of H is increased In the reverse direction, B
becomes 0 at C point and specimen gets completely demagnetized. This
value of H i.e. OC is called the coercive field Hc. This effect is called
COERCIVITY.
 If H is further increased in reverse direction, B also increase in reverse
direction and follows the path de instead of dc.
 Now, if H in increased in the main direction, specimen gets completely
demagnetized at f. Thus variation B with respect to H traced along the
closed path abcdefa in one full cycle of magnetization and
demagnetization is called the hysteresis curve.
 The area enclosed by the curve gives the energy loss per unit volume of
the material per cycle.

11. Hysteresis on the basis of
Domain

12. Thank
you…