Diamagnetism, Ferromagnetism and Paramagnetism

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Origin of Magnetism

The origin of magnetism is explained by taking into consideration the circular motion of electrons. The electrons present inside the atoms move in circular orbits around the nucleus; this is similar to a circular coil carrying current. The electron's orbital motion gives rise to the orbital magnetic moment.

The electrons tend to spin around in their own axis, thus creating a spin magnetic moment. The magnetic moment of an atom is the result of the vector sum of the orbital and spin magnetic moment. Based upon the magnetic properties, the magnetic substances are classified into three groups, namely diamagnetic, ferromagnetic, and paramagnetic.


Diamagnetic Substances 

Diamagnetic Definition

Diamagnetic substances are magnetized weakly when placed in an external magnetic field in a direction that is opposite to the applied field. The type of magnetism that is exhibited by these substances is known as diamagnetism. Examples of diamagnetic substances are copper, gold, antimony, bismuth, silver, lead, silicon, mercury, etc. 

The electron's orbital motion gives rise to an orbital magnetic moment. In addition to this, the electrons tend to spin around their own axis, creating a spin magnetic moment. Electrons in an atom can have a clockwise or anticlockwise spin. In a similar way, the electrons can revolve around the nucleus in a clockwise or anticlockwise direction.

In the case of diamagnetic substances, the magnetic moments of atoms and the orbital magnetic moments have been oriented in such a manner that the vector sum of an atom’s magnetic moment becomes zero.


Characteristics

  • In a diamagnetic substance, the magnetic moment of every atom is calculated to be zero.

  • An external magnetic field can repel them weakly.

  • If diamagnetic substances are placed in a non-uniform magnetic field, then the substances move towards the weaker side of the field from the stronger side.

  • When these substances are placed in an external magnetic field, they get weakly magnetized in the direction that is opposite to the direction of the field.

  • Magnetic susceptibility turns out to be negative in diamagnetic substances.


Ferromagnetic Substance

Substances that get magnetized strongly in an external magnetic field in a direction which is the same as the direction of the externally applied field are known as ferromagnetic substances. These types of substances retain their magnetic moment even after the removal of the magnetic field. Ferromagnetic substances tend to move from weaker to stronger parts of the external field. Some examples of ferromagnetic substances are iron, cobalt, and nickel.

In the ferromagnetic substances spin, magnetic moments have a large contribution. These substances consist of a large number of small units that are known as domains. These domains experience torque when a ferromagnetic substance is exposed to an external magnetic field. Due to this, the domains rotate and remain parallel to the direction of the field.


Characteristics

  • A large number of small domains make ferromagnetic substances.

  • These substances do not lose their magnetism when the external magnetic field is removed.

  • These substances become paramagnetic when they are heated above the curie point.

  • The external magnetic field strongly attracts ferromagnetic substances.

  • These ferromagnetic materials tend to move from the weaker to the stronger part of the field when the magnetic field is non-uniform.

  • If a rod of ferromagnetic substance is placed in a uniform magnetic field, the rod comes to rest with its length being parallel to the direction of the field.


Paramagnetic Substances

Substances that get magnetized weakly when placed in an external magnetic field in the same direction as the direction of the externally applied field are known as paramagnetic substances. These substances are different from ferromagnetic and diamagnetic substances. They have a tendency to move from the weaker to the stronger part of the magnetic field. Some examples of paramagnetic substances are calcium, lithium, tungsten, aluminium, platinum, etc.

In a paramagnetic substance, each atom has a permanent magnetic dipole moment because of the way they spin, the magnetic moments are oriented. However, the direction of magnetic moments can have random orientations when there is thermal motion. Due to which the net magnetic moment of this substance is zero.


Characteristics

  • Every atom in this substance is considered as a magnetic dipole that has a resultant magnetic moment.

  • The external magnetic field creates a weak attraction to these substances.

  • They move from weaker to the stronger part of the field when placed in a non-uniform field.

  • These substances lose their magnetism when the external magnetic field is removed.

FAQ (Frequently Asked Questions)

1. Differentiate Between Paramagnetic and Diamagnetic Substances.


Paramagnetic Substances

Diamagnetic Substances

The term paramagnetic refers to the attraction of material to an external magnetic field.

The term diamagnetic refers to the repulsion of material from an external magnetic field.

These substances have at least one unpaired electron.

These substances have no unpaired electrons.

Magnetic field direction is the same as that of the external magnetic field.

Magnetic field direction is opposite to the direction of the external magnetic field.

They exhibit stronger magnetic behaviour.

They exhibit weaker magnetic behaviour and easily get surpassed in the presence of stronger magnetic properties.

2. Differentiate Between Diamagnetic and Ferromagnetic Substances.


Ferromagnetic substances

Diamagnetic substances

These substances are always in a solid-state.

These substances can be in a solid, liquid, or gaseous state.

These substances are strongly attracted by magnets.

These substances are feebly repelled by magnets.

They move from the weaker to the stronger part of the field when placed in a non-uniform magnetic field.

They move from stronger to weaker parts of the field when placed in a non-uniform magnetic field.

They can turn into paramagnetic substances if heated above the curie point.

Temperature has no impact on these substances.