Ferromagnetic Material at Atomic Level

Q: 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.

Q: The magnetic susceptibility is negative for:

Hint: Magnetic susceptibility is a proportionality constant that determines the degree of magnetization of a material with respect to the applied magnetic field. Solution: Step1: The magnetic susceptibility denotes whether a material is repelled out or attracted of a magnetic field. It is negative only for diamagnetic material and it is positive for paramagnetic material and ferromagnetic material has large positive magnetic susceptibility. Hence option ‘A’ is correct.

Q: If the magnetizing field on a ferromagnetic material is increased, its permeability

The magnetic permeability of a substance is defined as \$\mu=\dfrac{B}{H}\$where \$B\$ is the established magnetic field inside the material,\$H\$ is the applied external magnetic field.When the external applied magnetic field \$H\$ is increased, the established magnetic field for a ferromagnetic material remains the same. Thus the magnetic permeability decreases.

Q: The variation of magnetic susceptibility with the temperature of a ferromagnetic material can be ploted as :

The magnetic susceptibility of ferromagnetic material in paramagnetic region is given by Curie-Weiss Law, which is presented as:\$\chi=\dfrac{C}{T-T_C}\$where \$T_C\$ is the critical temperature and \$\chi\$ is magnetic susceptibility at temperature \$T\$.Thus \$\chi\$ Vs \$T\$ graph is a hyperbola.Hence the correct representation of the curve is the option B.

Q: State and explain Curie's law.

Curie's Law:In a paramagnetic material the magnetization of the material is directly proportional to an applied magnetic field. However, if the material is heated, the magnetization is inversely proportional to temperature.i.e. M = C x ( B / T )where, M is the magnetisationB is the magnetic field, measured in teslasT is absolute temperature, measured in kelvinsC is a material-specific Curie constantIt was first discovered experimentally by French physicist, Pierre Curie. It holds for high temperatures, or weak magnetic fields.

Q: Draw hysteresis curve (B-H curve) for a ferromagnetic substance

Hysteresis curve for ferromagnetic substance * Ferromagnetic material has high retentivity & low coercivity

Q: A uniform magnetic field gets modifies as shown in Figure below , when two speciments X and Y are placed in it . Identyfy wether speciment X and Y are diagramatic , paramagnetic or ferromagnetic .

X is diamagnetic andY is ferromagnetic.X is diamagnetic as it expels magnetic lines Y is paramagnetic or ferromagnetic as it pulls the magnetic lines into it.

Q: Out of the two magnetic materials, 'A' has relative permeability slightly greater than unity while 'B' has less than unity. Identify the nature of the materials 'A' and 'B'. Will their susceptibilities be positive or negative?

For a paramagnetic material, the relative permeability lies between \$1 < \mu_r < 1 + \varepsilon \$ and its susceptibility lies between \$0 < X < \varepsilon \$.Hence, 'A' is a para-magnetic material and its susceptibility is positive. This is because its relative permeability is slightly greater than unity. For a diamagnetic material, the relative permeability lies between \$0 \leq \mu_r < 1\$ and its susceptibility lies between \$-1 < X < 0\$. Hence, 'B' is a diamagnetic material and its susceptibility is negative. This is because its relative permeability is less than unity. Here \$\mu_r\$ and \$x\$ refer to the relative permeability and susceptibility.

Q: In a permanent magnet at room temperature.

A permanent magnet at room temperature retains a ferromagnetic property that possesses a dipole moment. And domains are partially aligned due to thermal agitation.The correct option is C.

Physics

definition

Paramagnetic, diamagnetic and ferromagnetic materials

Paramagnetic materials have a small, positive susceptibility to magnetic fields. These materials are slightly attracted by a magnetic field and the material does not retain the magnetic properties when the external field is removed.
Diamagnetic materials create an induced magnetic field in a direction opposite to an externally applied magnetic field and are repelled by the applied magnetic field. It has a negative and small value of magnetic susceptibility.
Ferromagnetic materials have large magnetic susceptibility and are characterized by non-linear relation between magnetic field (