Draw the hysteresis curve ($B-H$ loop) and explain it.

(N/A) The relation between $\overrightarrow{B}$ and $\overrightarrow{H}$ in ferromagnetic materials is complex. It is non-linear and depends on the magnetic history of the sample.
The figure depicts the behavior of the material through one cycle of magnetization.
$1$. Initial Magnetization: Let the material be unmagnetized initially. We place it in a solenoid and increase the current. The magnetic field $B$ in the material rises and saturates as shown by the curve $O-a$.
$2$. Retentivity: Now,decrease $H$ and reduce it to zero. At $H=0$,$B \neq 0$. This is represented by the curve $a-b$. The value of $B$ at $H=0$ is called retentivity $(B_R)$. The domains are not completely randomized even though the external field is removed.
$3$. Coercivity: Next,the current in the solenoid is reversed and slowly increased. Certain domains are flipped until the net field inside is nullified. This is represented by the curve $b-c$. The value of $H$ at $C$ is called coercivity $(H_c)$.
$4$. Saturation: As the reversed current is increased in magnitude,we once again obtain saturation,represented by the curve $c-d$.
$5$. Completion of Cycle: Next,the current is reduced (curve $d-e$) and reversed (curve $e-a$). This cycle repeats itself.
Phenomenon: The curve $O-a$ does not retrace itself as $H$ is reduced. For a given value of $H$,$B$ is not unique but depends on the previous magnetization. This phenomenon is called hysteresis,which means 'lagging behind'.