Answer the following question: (a) Explain qualitatively on the basis of 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 ferromagnet is a device for strong memory? Explain the meaning of this statement.
(d) What kind of ferromagnet 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.

Explanation

(b) As energy dissipated per cycle is directly proportional to the area of the hysteresis loop, therefore, carbon steel piece will dissipate greater heat energy.
(c) Magnetisation of a ferromagnet depends not only on the magnetising field, but also on the history of magnetisation (i.e. how many cycles of magnetisation it has undergone). Thus value of magnetisation of a specimen is a record of memory of the cyles of magnetisation it has undergone. The system displaying such a hysteresis loop can thus act as a device for storing memory.
(d) The ceramic materials (specially treated barium, iron oxides) also called ferrites are used for coating magnetic tapes as memory tapes in a cassettle player, or for building memory stores in a modern computers.
(e) A space can be shielded from magnetic field by surrounding the space with soft iron ring. As magnetic field lines will be drawn into the ring, the enclosed region will become free of magnetic field.