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Paramagnetic substances get weakly magnetised or tend to get weakly magnetised along the direction of an externally applied magnetic field. Upon removing the magnetic field, the substance subsequently gets non-magnetized. They tend to have a permanent magnetic moment or a permanent dipole throughout. They have unpaired electrons in them. The net dipole in these substances is never zero. The permanency in the dipole moment is because of the randomization of the orientations of spins due to their thermal motions.
Paramagnetism
This phenomenon is found in para magnetic substances. Paramagnetism is when the 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 these substances is never zero due to unpaired electrons in them. This is the reason why they have a permanent dipole. On applying a magnetic field, this dipole gets oriented in the direction of that field.
Paramagnetism is mainly classified into two categories –
- In the first category, the magnetic moment or the dipole is found in very low concentrations, leading to their separation. In this type, the spins also do not interact with each other.
- In the second category, this phenomenon occurs due to the spins interacting. Although it is feeble, there is an interaction between the dipole or magnetic moment.
Although how they get magnetised is entirely based on a law known as Curie’s law. It states that the magnetic susceptibility of these materials is not directly proportional to temperature. For example, if the temperature increases, the magnetic susceptibility will decrease and vice versa.
Properties of paramagnetic substances
There are certain properties of these kinds of materials. They are –
- The atoms of these materials 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 presence of a non-uniform magnetic field.
- If a paramagnetic liquid is placed in a U tube, it starts to ascend gradually to the poles because of the presence of magnets.
- Since the magnetic field is much stronger near the poles, the para magnetic rods align themselves along the direction of the magnetic field.
- In paramagnetic substances, the magnetic susceptibility is small yet positive.
- These substances have a small but positive intensity of magnetization, so they always orient themselves in the magnetic field’s direction.
- Magnetic field lines tend to get denser when observed inside a paramagnetic material.
- The magnetic field inside the substance is higher than the external magnetic field. This is why these substances have a relative permeability that is a little greater than 1.
- The magnetic susceptibility of these materials is not directly proportional to temperature.
There are experiments conducted worldwide where a para magnetic 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 get accumulated in the centre because the magnetic field is pretty strong in the middle because of this unique phenomenon. Again, when the liquid in the watch glass is placed between two magnets that are wide apart, they start to move towards the two respective poles of the same magnet due to the strong magnetic field.
Examples of paramagnetic substances
Paramagnetic materials are those that show magnetic susceptibility that obeys Curie’s law. Sometimes they even show paramagnetism irrespective of any temperature range. Some of the paramagnetic materials include titanium, iron oxide, tungsten, sodium, aluminium, oxygen, magnesium, lithium, and transition metal complexes, to name a few.
Super-para magnetic materials
They are the ones who not only exhibit the phenomenon of paramagnetism but also show strong ferromagnetic or ferrimagnetic behaviour when they are placed in an externally applied magnetic field at the microscopic level. They not only obey Curie’s law but also have huge Curie constants. Ferrofluids is one such example.
Conclusion
Paramagnetic substances show a feeble magnetization in the direction of the magnetic field. When the magnetic field is removed, their magnetization also decreases. They 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 randomization in their spin orientation. These substances get magnetised following Curie’s law. Temperature plays an important role to what extent they will be magnetised. Some of the most common paramagnetic materials are tungsten, iron oxide, oxygen, sodium, magnesium, etc. numerous experiments have been done to demonstrate this phenomenon in these substances.
