Para-, dia- and ferro-magnetic substances

Electrons are found in pairs in most atoms. When electrons are coupled together, their magnetic fields cancel each other out due to their opposite spins. And so, there is no net magnetic field there. Materials having some unpaired electrons, on the other hand, will have a net magnetic field and respond more to an external field. The majority of materials can be classified as diamagnetic, paramagnetic, and ferromagnetic materials.

According to their bulk magnetic susceptibility, all materials can be classified into one of three categories based on their magnetic behaviour as ferromagnetic, diamagnetic or paramagnetic material. Diamagnetism and paramagnetism are the two most frequent types of magnetism, and they account for the magnetic properties of most of the elements in the periodic table at room temperature.

In the absence of an implemented area, dipole moments are oriented randomly and consequently, the object has no net macroscopic magnetisation. In paramagnetic substances, localised magnetic moments are present. However, they no longer showcase net microscopic magnetisation in the absence of an implemented area. There are forms of paramagnetism. In one, the magnetic moments are present at sufficiently low attention in order that they’re nicely separated from each other, and their spins no longer interact.

Diamagnetism

Diamagnetism is the tendency of a substance to oppose an applied magnetic field and hence, to repel the applied magnetic field. It can be found in all materials. The paramagnetic behaviour, on the other hand, predominates in a material having paramagnetic qualities (that is, a tendency to amplify an external magnetic field). Diamagnetic behaviour is thus exhibited exclusively in a completely diamagnetic substance, despite its universal presence. Because there are no unpaired electrons in a diamagnetic material, the inherent electron magnetic moments cannot generate a bulk effect. The magnetisation in these instances is caused by the orbital motions of the electrons.

When there is no applied field, the atoms in a diamagnetic substance have no net magnetic moment. The spinning electrons process under the influence of an applied field (H), and this motion, which is a form of electric current, causes a magnetisation (M) in the opposite direction of the applied field. Although all materials have a diamagnetic effect, the diamagnetic effect is sometimes obscured by the larger paramagnetic or ferromagnetic term. The temperature has no effect on the value of susceptibility.

Diamagnetic materials produce a magnetic response opposite to the applied field and, therefore, turn at a right angle to the field.

Characteristics of diamagnetic materials:

1. The magnetic moment of each atom in a diamagnetic substance is calculated to be zero.

2. They can be repelled by a weak magnetic field.

3. Diamagnetic substances shift from the stronger to the weaker side of the field when they are placed in a non-uniform magnetic field.

4. When these materials are exposed to an external magnetic field, they become weakly magnetised in the opposite direction as the field.

5. In diamagnetic materials, magnetic susceptibility is shown to be negative.

6. Diamagnetism occurs in substances such as copper, silver, gold etc.

Paramagnetism

The electron spin of unpaired electrons causes paramagnetism. When a group of electrons is subjected to a magnetic field, the dipole moments of the electrons seem to line up with the field, just like a tiny bar magnet. The effect boosts net magnetisation in the applied field’s direction. Paramagnetism, like diamagnetism, is weak and only exists in the presence of an applied field; however, because the effect boosts the applied field, the paramagnetic susceptibility is always positive. A paramagnetic substance’s susceptibility ranges from 10⁻⁴ to 10⁻⁶ emu/cm³.

Paramagnetic materials align themselves with the applied field.

Unpaired electrons, or atomic or molecular orbitals containing exactly one electron, exist in paramagnetic materials. While the Pauli exclusion principle requires paired electrons to have their inherent (‘spin’) magnetic moments pointing in opposite directions to cancel out their magnetic fields, an unpaired electron can orient its magnetic moment in any direction. When a magnetic field is present externally, these magnetic moments try to equate in the same direction as the applied field, strengthening it.

Characteristics of paramagnetic materials:

1. Every atom in this substance is thought to be a magnetic dipole with a magnetic moment as a result.

2. These materials are attracted to the external magnetic field via a weak attraction.

3. When placed in a non-uniform field, they travel from the weaker to the stronger area of the field.

4. When the external magnetic field is removed, these materials lose their magnetism.

5. Paramagnetism occurs in substances such as lithium, tantalum and magnesium.

Ferromagnetism

Because of the electron’s magnetic properties, ferromagnetism also exists. Unlike paramagnetism, ferromagnetism can exist even when there is no external field. Because it is energetically advantageous, the magnetic dipole moments of the atoms naturally lineup with one another. It is possible to keep a remanent magnetisation. Absolute zero (0 K, or -273.15° C) is the only temperature at which the dipole moments can be perfectly aligned. Thermal motions begin to disrupt magnetic moments above absolute zero. 

The thermally produced disorder overcomes the alignment at a temperature called the Curie temperature, which varies from material to material, and the substance’s ferromagnetic qualities vanish. Ferromagnetic materials have a high susceptibility and also a positive one. It ranges between 10 and 104 emu/cm3. They have a large, positive susceptibility to an external magnetic field. They have a strong attraction to magnetic fields, and they are also able to retain their magnetic properties even after the external field has been removed.

Characteristics of ferromagnetic materials:

1. Ferromagnetic compounds are made up of a high number of tiny domains.

2. When the external magnetic field is removed, these substances retain their magnetism.

3. When heated over the curie point, certain materials become paramagnetic.

4. Ferromagnetic compounds are highly attracted by the external magnetic field.

5. When the magnetic field is non-uniform, these ferromagnetic materials tend to shift from the weaker to the stronger section of the field.

6. When a ferromagnetic rod is placed in a homogeneous magnetic field, it will come to rest with its length parallel to the field’s direction.

Ferromagnetism only occurs in some substances like iron, cobalt, nickel, their alloys, and some alloys of rare-earth metals.

If we talk about the permeability of diamagnetic, paramagnetic and ferromagnetic materials, it will be little less than unity for diamagnetic materials, little more than unity for paramagnetic materials and very high for ferromagnetic materials.

Diamagnetism results from an imbalance of the orbital pairing of electrons, whereas paramagnetism is a result of an imbalance of the spin pairing of electrons.

Conclusion 

Materials can be classified into three categories based on their magnetic properties: diamagnetic, paramagnetic, and ferromagnetic materials. The primary difference between diamagnetic, paramagnetic, and ferromagnetic materials is that diamagnetic materials are not attracted to external magnetic fields, whereas paramagnetic materials are attracted to external magnetic fields, and ferromagnetic materials are highly attracted to external magnetic fields.

Since diamagnetic materials repel magnetic fields, they are easily distinguishable from other materials. Paramagnetic and ferromagnetic materials can be separated with the help of induced roll magnetic separators by varying the strength of the magnetic field utilised in the separator.