Properties of Diamagnetic Materials

The magnetic forces of a material’s electrons will be changed when put in a magnetic field. Faraday’s law of magnetic induction describes this phenomenon. The magnetic properties determine how it responds to an external magnetic force. 

Materials are classified into three types by their response to externally applied magnetic fields: diamagnetic, paramagnetic, or ferromagnetic fields. Atoms of materials that show diamagnetic behaviour have no permanent magnetic dipole moment.

When a diamagnetic material is introduced in an external magnetic field, a weak and slim magnetic dipole moment is induced in the direction of the applied field. Without applying a magnetic field, diamagnetic materials have no net magnetic moment (H). The spin motion of electrons and their interactions with one another are the origins of magnetism. 

When diamagnetic material is subjected to an external magnetic field, the spinning electrons undergo a motion that produces an electrical current, resulting in magnetisation in the opposite direction of the magnetic field. 

When an electron in an atomic orbit moves through a magnetic field, the force applied on the electron causes a slight shift in orbital motion; the electron orbit processes around the magnetic field’s direction. The properties of diamagnetic materials vary in nature.

What are the different types of magnetic properties?

The magnetic properties possessed by the atoms and ions of a material are responsible for the magnetic properties shown by the material. The revolution of the atoms around the nucleus of the atom and the spin of the electrons in their axis causes the magnetic properties of the materials. Materials are classified into five types depending on their magnetic properties. They include:

1. Paramagnetic- The magnetic field magnetises at least one pair of unpaired electrons in its orbit shell, causing paramagnetism.
2. Diamagnetic – Diamagnetism is induced magnetism that occurs when materials are subjected to a high magnetic field.
3. Ferromagnetic- When magnetic moments are aligned in both directions (parallel and antiparallel), but in uneven amounts, ferromagnetic substances form.
4. Antiferromagnetic- Antiferromagnetism is magnetism in which neighbouring atoms’ magnetic moments are aligned antiparallel.
5. Ferrimagnetic- Magnetic moments of domains in ferrimagnetic substances are aligned in uneven quantities in parallel and antiparallel directions.

What Causes Diamagnetism?

The orbital motion of electrons produces magnetic fields by creating atomic current loops. When a material that shows the diamagnetic property is subjected to an external magnetic field, the current spins will tend to arrange themselves to act opposite to the applied field. 

In diamagnetism, electrons inside a material respond to an external magnetic field by rotating rapidly, creating magnetic forces opposing the external field. All materials are diamagnetic to some degree since all atoms contain electrons. However, if diamagnetism is present, the greater forces of paramagnetism or ferromagnetism will quickly outnumber it. All these are together responsible for the different properties of diamagnetism.

Properties Of Diamagnetic Materials

Susceptibility

When a substance is put in an external magnetic field, its susceptibility measures how much it becomes magnetised.  

The magnetic susceptibility of a material is denoted by the Greek letter chi (χ).

It is expressed as the magnitude of the internal polarisation (J) divided by the strength of the external field (B0): 

χ = J / B0

Diamagnetic materials resist the magnetic field; hence magnetic susceptibility is negative for diamagnetic materials. The spin in a diamagnetic substance is aligned in the opposite direction of the applied magnetic field. The value of susceptibility is not dependent on temperature.

Permeability Of Diamagnetic Substances

The capacity of diamagnetic materials to reject force lines is known as permeability (due to the structure of diamagnetic material). They reject force lines and prevent magnetic lines of force from passing through them. As a result, the 1 for diamagnetic materials.

The ratio of internal magnetisation to the applied magnetic field is measured by magnetic permeability.

When diamagnetic material is placed in a magnetic field, the magnetic force lines prefer not to pass through it as if the diamagnetic substance was ejecting magnetic field lines. As a result, the sample’s magnetic field lines reduce to a lesser value.

Points to remember in Diamagnetic materials

• In a non-uniform magnetic field, diamagnetic materials shift from a strong intensity to a weaker location. That suggests the magnetic field is only weakly repelling them.
• In fluctuating magnetic fields, any conductor will exhibit a high diamagnetic effect because circulating currents will be created in the conductor by the fluctuations in the magnetic field. Because there is no resistance to forming current loops in a superconductor, it will be a perfect diamagnet.
• Another property of diamagnetic materials is that because the field is strongest at the ends, a rod of diamagnetic material suspends in a homogenous magnetic field with its length set 90 degrees to the field direction.
• Diamagnetic materials don’t have atomic dipoles because the resulting magnetic moment of each atom is zero owing to paired electrons.
• In diamagnetism, the magnetic moment per unit mass in a given field remains constant for a particular substance throughout a wide range of temperatures.
• When diamagnetic materials are put in a non-uniform magnetic field, they shift from the stronger to the weaker areas of the field.
• Lead, Carbon, and Bismuth are some examples of diamagnetic materials.

Conclusion

Magnetic fields have a weak and negative susceptibility in diamagnetic materials. When a magnetic field is applied, diamagnetic materials are somewhat repelled and lose their magnetic qualities when the field is withdrawn. Diamagnetic materials are made up of atoms with no net magnetic moments. Only if there are no other magnetic effects present, such as ferrimagnetism, whose susceptibility is substantially higher in most circumstances, does a material’s diamagnetic response contribute to its magnetisation. Diamagnetism exists in all materials. It is temperature independent and is often disregarded since it is so little compared to ferromagnetic and paramagnetism effects.