What Are Para magnetic Liquids?

Paramagnetic substances, such as liquids, are very weakly magnetised in the direction of an externally applied magnetic field. They lose their magnetic properties when the field is removed. They tend to orient themselves where they feel the magnetic field more strongly. Paramagnetic liquids have a permanent magnetic moment or dipole because of the presence of an unpaired electron in their atom. That is why the net dipole moment of these liquids never actually comes to zero. A possible explanation for the permanent dipole is the thermal motions that tend to randomise their spin orientation.

Paramagnetism and Its Effects

Paramagnetism is the phenomenon where a substance tends to get weakly magnetised upon an external field, unlike ferromagnets that strongly get magnetised in an external magnetic field. 

The net magnetic moment in them is never zero due to unpaired electrons in their atoms. This is why they have a permanent dipole. On applying a magnetic field, this dipole gets oriented in the direction of that field. When the magnetic field is removed, the substance loses its magnetisation.

How the paramagnetic liquids get magnetised is entirely based on a law known as Curie’s law. It states that the magnetic susceptibility of the paramagnetic materials has an inverse relation with temperature. For example, if the temperature increases, the magnetic susceptibility will decrease. If the temperature decreases, it leads to an increase in magnetic susceptibility.

Examples of paramagnetic Liquids

Some para magnetic materials include: 

• Titanium
• Iron oxide
• Tungsten
• Sodium
• Aluminium
• Oxygen
• Magnesium
• Lithium
• Manganese
• Transition metal complexes

Dysprosium nitrate, manganese salts such as manganese nitrate, manganese chloride or manganese sulphate are paramagnetic salts that are cheap and easily available. They can be used to prepare paramagnetic liquids. Another example is liquid oxygen, which also exhibits paramagnetic behaviour.

Properties of paramagnetic Liquids

• The atoms of these liquids tend to have a permanent magnetic moment or dipole due to their unpaired electrons present inside them. 
• They are feebly magnetised in the direction of an externally applied magnetic field. 
• They tend to move from a weak field magnetic region to a stronger magnetic region in the presence of a non-uniform magnetic field. 
• These liquids have a small but positive intensity of magnetisation, which is why they always orient themselves in the magnetic field’s direction. 
• The magnetic field inside the liquids is higher than the external magnetic field. This is why these liquids have a relative permeability that is a little greater than 1.
•  The magnetic susceptibility of the paramagnetic liquids has an inverse relation to temperature.

How to Prepare a paramagnetic Liquid

• To make a paramagnetic liquid, we need a salt that exhibits paramagnetism. 
• For example, salts of manganese like manganese sulphate or manganese chloride or manganese nitrate are cheaper and easily available. Unlike ferromagnets, they are weakly magnetised when a magnet is brought close to them.
• To make a liquid, we need to make a dispersion medium, like dichloromethane. Dichloromethane is dense, so we need to saturate it by adding an adequate amount of water. 
• The entire medium is prepared using dichloromethane, water, and manganese salts in accurate proportions. The resulting liquid is a para magnetic liquid. 
• Upon bringing a magnet nearby, the manganese starts to show paramagnetic behaviour and forms a droplet attracting towards the field. 

Demonstration of paramagnetic Liquid

• A paramagnetic liquid is placed in a watch glass between two poles of a nearby magnet. 
• After some time, it is observed that the liquid starts to accumulate in the centre because the magnetic field is strong in the middle. 
• Again, the liquid in the watch glass is placed in between two magnets that are wide apart.
• The liquid starts to move towards the two respective poles of the same magnet owing to the strong magnetic field at the poles.

Conclusion

Paramagnetic substances have a permanent dipole or magnetic moment in them. This is because of the presence of unpaired electrons in their atoms. The permanent dipole is because of the thermal motions that cause randomisation in their spin orientation. 

Paramagnetic liquids often get accumulated in the middle due to strong magnetic fields in the centre. They also move towards poles when they are far away. Some paramagnetic liquids include liquid oxygen and salts of manganese in a denser dispersion medium like dichloromethane. 

These liquids are magnetised following Curie’s law. Temperature plays an important role to what extent they will be magnetised.