5.5.2. Paramagnetism

Paramagnetic substances are those which get weakly magnetised when placed in an external magnetic field. They have a tendency to move from a region of weak magnetic field to strong magnetic field, i.e., they get weakly attracted to a magnet.

Paramagnetic materials exhibit a weak form of magnetism. When they are exposed to an external magnetic field, they experience a slight magnetization. This means that paramagnetic substances will align themselves, albeit weakly, to the direction of the magnetic field. This effect is not strong enough to create a permanent magnet but is enough to make these materials move towards regions of stronger magnetic fields.

Think of paramagnetic materials like tiny, weak magnets that only respond to a much stronger magnet. For instance, if you have a weak magnet such as a paper clip, it won't stick unless you bring it near a stronger magnet like a refrigerator magnet. Similarly, once the external magnet is removed, the paper clip will lose its magnetic attraction.

The individual atoms (or ions or molecules) of a paramagnetic material possess a permanent magnetic dipole moment of their own. On account of the ceaseless random thermal motion of the atoms, no net magnetisation is seen.

Each atom in a paramagnetic material has its own tiny magnet due to unpaired electrons. However, because these atoms are constantly moving around due to thermal energy, their magnetic moments are oriented randomly, resulting in no net magnetization. When a strong external magnetic field is applied, it can align these atomic dipoles, leading them to point in the same direction, and thus showing a measurable magnetization.

Imagine a room full of people (the atoms) who are all facing different directions. If a loud announcement comes (the external magnetic field), everyone starts turning to face the same direction. Before the announcement, there’s chaos (no net magnetization) but after, there’s alignment and organization (net magnetization).

In the presence of an external field B0, which is strong enough, and at low temperatures, the individual atomic dipole moment can be made to align and point in the same direction as B0.

Temperature affects paramagnetism significantly. At higher temperatures, the random thermal motion of the atoms increases, which can disrupt alignment in a magnetic field. However, at lower temperatures, the thermal agitation decreases, allowing the dipoles to align more effectively with the external magnetic field. Thus, low temperature combined with a strong magnetic field leads to stronger magnetization.

Think of it like a crowd trying to form a line for a concert. When it’s warm outside (high temperature), people are more restless and scattered. However, if it gets cooler (lower temperature), they start to settle down and align more easily, allowing them to form a neat line (alignment with the magnetic field).

When placed in a non-uniform magnetic field, the bar will tend to move from weak field to strong.

In non-uniform magnetic fields, the strength of the magnetic field varies across space. Paramagnetic materials will experience a net force that causes them to move toward regions of higher magnetic field strength. This behavior is due to the tendency of the magnetic dipoles to align with the stronger field, resulting in a net attraction.

Consider a leaf being blown by the wind into a stronger breeze. Just as the leaf will move toward the area where the wind is strongest, paramagnetic materials will move toward regions where the magnetic field is stronger.

Some paramagnetic materials are aluminium, sodium, calcium, oxygen (at STP), and copper chloride.

Examples of paramagnetic materials include metals like aluminium and sodium, as well as gases like oxygen. These materials display weak magnetism, and their behavior can be utilized in various applications, from manufacturing to scientific experiments.

Think of these materials like the side characters in a story. They might not be the main characters (powerful magnets), but they play significant supportive roles when a stronger character (external magnetic field) is present. For instance, oxygen in the air contributes to paramagnetism but only shows it under specific conditions, like in strong fields and low temperatures.

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