Question

2. Describe the Weiss theory of ferromagnetism. Discuss the temperature dependence of spontaneous magnetisation​

Answer 1

Answer:

He postulated that the neighboring atoms of the ferromagnetic materials, due to certain mutual exchange interactions, from several number of very small regions, called domains. ... Weiss theory of ferromagnetism is also called domain theory of ferromagnetism.

The decrease in spontaneous magnetization at higher temperatures is caused by the increasing excitation of spin waves. In a particle description, the spin waves correspond to magnons, which are the massless Goldstone bosons corresponding to the broken symmetry.

Answer 2

The decrease in spontaneous magnetization at higher temperatures is caused by the increasing excitation of spin waves. ... Hence the magnetization of an anisotropic magnet is harder to destroy at low temperature and the temperature dependence of the magnetization deviates accordingly from the Bloch's law.