Paramagnetism is the phenomenon that occurs when an external magnetic field weakly attracts some materials. This creates induced magnetic fields within them in the direction of the applied field. Michael Faraday first discovered paramagnetism in 1845.

Paramagnetic materials are weakly magnetised in the direction of an applied magnetic field. When a magnet is applied to these materials, they are weakly attracted. With a temperature rise, magnetic materials tend to lose their magnetic properties.

The materials will lose their magnetic properties if the applied field is removed.

Electron spin orientations are randomised by thermal motion. Examples of paramagnetic materials are lithium, magnesium, oxygen, aluminium, molybdenum, sodium, tantalum etc. 

The Theory Behind Para Magnetism

• The characteristics of paramagnetic materials are due to at least one unpaired electron spin in their atoms and molecules. 
• A paramagnetic material is a material whose atoms have incompletely filled atomic orbitals. 
• The spin of the unpaired electrons creates a magnetic dipole moment. These unpaired electrons act as magnets within the material. 
• Their spin aligns with the field whenever the electrons are exposed to an external magnetic field. 
• The material is attracted to the field since all unpaired electrons line up in the same direction. 
• If the external field is removed, the spins return to their original orientation when the external field is not present.  

Curie’s law

Following Curie’s law, the magnetisation of a paramagnetic material appears inversely proportional to the absolute temperature of the material. In other words, the magnetic susceptibility of a paramagnetic material appears directly proportional to the inverse of absolute temperature. 

I.e., M = C B0 /T

Since, B0 = μ0 H                 

so, M = C μ0 H / T 

or, M / H = μ0 C / T

But M / H = χm                   

therefore, χm = μ0 C / T   

or, χm ∝ 1 / T

Where M = magnetization, χ is magnetic susceptibility, B0 = magnetic field in Vacuum, C = Curie constant, H is the intensity of the magnetising field, and T is the absolute temperature.

Paramagnetic Materials

Paramagnetic materials are weakly magnetised in the direction of an applied magnetic field. In paramagnetic materials, some electrons are unpaired. These unpaired electrons cause the net magnetic moment of an atom to not add up to zero. A dipole is created in this case. Upon applying a magnetic field externally, the atomic dipole aligns with the direction of the magnetic field. Gases, liquids, and solids are all capable of exhibiting paramagnetic properties.

Paramagnetic materials are of two types: 

• Magnetic moments are separated in the first type because of the low concentrations of magnetic moments.
• Furthermore, the spins of these particles do not contribute to magnetism.
• Para Magnetism occurs due to the interaction between magnetic moments in the second type. These interactions are quite weak, however.
• Thus, when no field is applied, no net magnetisation occurs.

Properties of Paramagnetic materials

• The unpaired spin of the atom results in the permanent dipole moment of paramagnetic substances when the net atomic dipole moment is not zero.
• Paramagnetic substances move from a weak field area to a strong field area in a non-uniform external magnetic field.
• As the field is strongest near poles, a paramagnetic rod will line up parallel.
•  A paramagnetic liquid in a U-Tube rises on the limb of the tube between the magnet’s poles.
• There is a small, positive and directly proportional intensity of magnetisation to the magnetising field.
• Relative permeability is slightly over 1.
• There is a greater density of magnetic field lines inside paramagnetic materials.
• The magnetisation of a paramagnetic material is inversely proportional to the absolute temperature of the material.
• A paramagnetic substance has a small magnetic dipole moment parallel to its magnetising field.

The Importance of Para Magnetic force

• The Para Magnetic force magnetises the paramagnetic materials weakly, and those materials are attracted to strong magnets.
• Super paramagnet – A superparamagnetic material shows paramagnetic properties and strong ferromagnetic properties at the microscopic level. The Curie law also applies to these materials, and their Curie constants are very large. Superparamagnetic material like Iron oxide can be used as a coating or filler to enhance a device’s ability to respond to external magnetic fields.

Paramagnetic Liquid

In a watch glass placed between two poles, if a paramagnetic liquid is added, the liquid will accumulate at the centre, where the magnetic field is strongest.

If the watch glass is placed on two sufficiently different poles, the paramagnetic liquid will gather on the sides of the watch glass and show depression in the middle since the field is strongest at the poles.

Conclusion

Para Magnetism includes materials that are weakly attracted to a magnetic field applied externally. These materials form magnetic fields in the direction of the applied magnetic field. Michael Faraday, a British scientist who began his research into Paramagnetism in 1845, named that phenomenon and studied it extensively.

A paramagnetic material is a material that is weakly magnetic in the direction of a magnetic field applied. Magnets are weakly attracted to these materials. The magnetic properties of magnetic materials deteriorate with increasing temperature.