The only property possessed by ferromagnetic substances is

$A$ metal rod is subjected to cycles of magnetisation at the rate of $42 \ Hz$. The density of the metal is $6 \times 10^3 \ kg \ m^{-3}$ and its specific heat capacity is $0.1 \times 10^3 \ cal \ kg^{-1} \ ^{\circ}C^{-1}$. If the area of its $B-H$ loop corresponds to an energy density of $10^{-2} \ J \ m^{-3}$,then the rise in its temperature in one minute is: (in $^{\circ} C$)

Answer the following questions:
$(a)$ Explain qualitatively on the basis of the domain picture the irreversibility in the magnetisation curve of a ferromagnet.
$(b)$ The hysteresis loop of a soft iron piece has a much smaller area than that of a carbon steel piece. If the material is to go through repeated cycles of magnetisation,which piece will dissipate greater heat energy?
$(c)$ '$A$ system displaying a hysteresis loop such as a ferromagnet,is a device for storing memory?' Explain the meaning of this statement.
$(d)$ What kind of ferromagnetic material is used for coating magnetic tapes in a cassette player,or for building 'memory stores' in a modern computer?
$(e)$ $A$ certain region of space is to be shielded from magnetic fields. Suggest a method.

The coercivity of a magnet,where the ferromagnet gets completely demagnetized,is $3 \times 10^{3} \text{ A m}^{-1}$. The minimum current required to be passed in a solenoid having $1000 \text{ turns m}^{-1}$,so that the magnet gets completely demagnetized when placed inside the solenoid,is:

The figure illustrates how $B$,the flux density,inside a sample of ferromagnetic material varies with external magnetic field $B_0$. For the sample to be suitable for making a permanent magnet,

For substances,hysteresis $(B-H)$ curves are given as shown in the figures. Which of the following is best for making a temporary magnet?