Explain ferromagnetism on the basis of domain theory?
Weiss proposed a concept of ferromagnetic domains. According to his postulate neighboring atoms of the ferromagnetic materials due to interactions from several number of very regions. Those regions were called domains. His theory is also named as domain theory of ferromagnetism.
The domains are aligned along the direction of the applied magnetic field grow in size that is they align opposite to the field direction which gets reduced. In the presence of a weak external field, the magnetization in the material occurs mostly by the process of domain growing. In the presence of a strong magnetic field, the material gets magnetized by the process of alignment. When the field is removed the boundaries of domain do not recover their original position and the material is not completely demagnetized but some magnetism still remains.