Question
Explain ferromagnetism and ferromagnetic substances.
✓
Answer
→Ferromagnetic substances are those which get strongly magnetised when placed in an external magnetic field.
→The individual atoms in a ferromagnetic material possess a dipole moment as in a paramagnetic material.
→The neighbouring atoms are bound by strong attraction force. This bonding however, is limited to a small region. The atoms (molecules) in such small regions (small microscopic volumes) interact in such a way that their dipole moments are aligned in a common direction.
Such regions (macroscopic volumes) are called domain(s).
→Each domain has some net magnetisation. But the magnetisation varies randomly from domain to domain, and there is no bulk magnetisation.
→Typical domain size is 1 mm and the domain contains about $10^{11}$ atoms.
→When external magnetic field $\left(\overrightarrow{ B _0}\right)$ is applied, the domains orient themselves in the direction of $\vec{B}_0$.
→Simultaneously the domain oriented in the direction of $\overrightarrow{B_0}$ grow in size. As shown in fig. (b) all domains merge gradually and make a larger/'giant' domain.
→Thus, in a ferromagnetic material, field lines are highly concentrated.
→When such materials are placed in non-uniform magnetic field, they are attracted towards strong magnetic field.
→Examples : Some Ferromagnetic materials such as iron, cobalt, nickel, gadolinium etc. have relative magnetic permeability $>1000$.
→The individual atoms in a ferromagnetic material possess a dipole moment as in a paramagnetic material.
→The neighbouring atoms are bound by strong attraction force. This bonding however, is limited to a small region. The atoms (molecules) in such small regions (small microscopic volumes) interact in such a way that their dipole moments are aligned in a common direction.
Such regions (macroscopic volumes) are called domain(s).
→Each domain has some net magnetisation. But the magnetisation varies randomly from domain to domain, and there is no bulk magnetisation.
→Typical domain size is 1 mm and the domain contains about $10^{11}$ atoms.
→When external magnetic field $\left(\overrightarrow{ B _0}\right)$ is applied, the domains orient themselves in the direction of $\vec{B}_0$.
→Simultaneously the domain oriented in the direction of $\overrightarrow{B_0}$ grow in size. As shown in fig. (b) all domains merge gradually and make a larger/'giant' domain.
→Thus, in a ferromagnetic material, field lines are highly concentrated.
→When such materials are placed in non-uniform magnetic field, they are attracted towards strong magnetic field.
→Examples : Some Ferromagnetic materials such as iron, cobalt, nickel, gadolinium etc. have relative magnetic permeability $>1000$.
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