1. Ferro magnetism is a phenomenon by which spontaneous magnetization occurs, when T≤θ and so even in the absence of applied field, the magnetic moments are enormous. Here θ is the curie temperature of the material.
2. Ferromagnetism arises when the exchange energy is favorable for spin alignment
3. If a material acquires a relatively high magnetization in a weak field, then it is ferromagnetic
4. Magnitude of Susceptibility is very large and positive.
5. When temperature is greater than Curie temperature ‘θ’ then it is converted into paramagnetic.
6. When temperature is less than ‘θ ‘, the material is in ferromagnetic state and is very large due to spontaneous magnetization.
7. Due to the large internal field, the permanent dipoles are strongly aligned in the same direction and consequently a large spontaneous magnetization results even in the absence of an applied field.
8. They attract the lines of forces very strongly (fig 4.1(d)).
9. They exhibit magnetization even when the magnetizing field is removed. i.e. they exhibit magnetic hysteresis.
10. During heating they lose their magnetization slowly.
11. Spin alignment:
Eg:
Fe, Ni, Co
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