Question

What is the reason that a typical ferromagnetic material without applied field usually forms many small magnetic domains, instead of just a single big domain. Hint: To form a magnetic domain wall costs energy (exchange energy & anisotropy energy); a single big domain saves free energy

Answer 1

Answer :-

According to the domain theory, a deromagnetic substance consists of a large number of small units known as domains. A domain is exteranly small region containing a large number of atomic magnets having magnetic axes aligned in the same direction due to a strong exchange. coupling when a terromagnetic substance is kept in the magnetic filed, the permanent alignment of domain due to the a strong interaction (force) takes place this force is known as exchange couping.

In one domain the magnetic dipole moments of all the atoms are aligned in the same direction hence each domain has a resultant magnetic dipole moment the permanent arrangement is due to a strong ineteraction (once) known as exchange coupling.